Animal Anatomy and Physiology 2
Assignment 2500 words March 2016 50%
-Anatomy & physiology of a quadruped (horse) based upon structure and function of the
endocrine and nervous system.
-Importance of Homeostatic principles and the regulation of function of the two systems
Exam @ university (after easter) 2 hours 50%
Create a glossary
Refer back to Learning Objectives find weak areas + example exam questions?
Homeostasis
Homeostasis: “The coordinated physiological processes which maintain most of the
[constant] states in the organism” Hill et al (2012)
Homeostasis: “the tendency for living things to attempt to maintain a state of relative
stability. At either a whole-animal level or at a cellular level.” Frandson et al (2008)
Homeokinesis: Mechanisms maintaining a relatively stable but constantly changing state
of the body
-Behavioural Freedom = allows mammal’s freedom to conduct their lives regardless of
outside conditions
-Healthy functioning = thermoregulation, osmoregulation, excretion, maintaining blood
glucose levels, blood pressure, pH etc
Regulation:
Advantages
Disadvantages
Mammal independent of variations in outside
climate
Costs energy
Conformity:
Advantages
Disadvantages
Energetically
Cheap
Cells within body subject to change when outside conditions
change
Osmoregulation (physiology and metabolic)
Thermoregulation (behaviour and physiology)
Blood glucose
Homeostatic Challenges:
-Diabetes in companion animals
-Thermoregulation in production pigs
-Fevers
-Dehydration
-Blood pressure in stressed animals
-Cell Death
-Behavioural/Psych problems
-Chronic stress in captives
Thermoregulation
Two types of organism:
-Endotherms: Organisms that gain heat from their internal metabolism (warm blooded eg.
mammals)
-Ectotherms: Organisms that gain heat from their environment (cold blooded eg. Reptiles)
Homeothermic
37⁰C: Optimal body temperature
Higher above this:
-Protein denaturation
-Nerve malfunction
-41⁰C can cause convulsion
-43⁰C absolute limit in most animals – death?
Heat Loss & Gain
-Radiation (gain & loss)
-Conduction (gain & loss)
-Convection (gain & loss)
-Evaporation (loss)
Physiological Adaptions to Prevent Heat Loss
-Hair/fur – eg. Polar Bears
-Feathers – trap air
-Adipose tissue – eg. Blubber (seals, whales)
Behavioural Responses to Prevent Heat Loss
-Curl up (reduction of surface area
-Group together
-Make nests
-Seek heat
Effector Mechanisms to Prevent Heat Loss/Increase Heat
Generation
-Vasoconstriction = decrease in blood vessel diameter
-Reductions
Effector Mechanisms to Prevent Heat Loss/Increase Heat
Generation
-Shivering and Increased voluntary activity
-Increased secretion of epinephrine (adrenaline)
-Increased food appetite
Autonomic Nervous System Control
Sympathetic (hot)
-Contracts erector pili muscles
-Increases sweat production
-Increases ventilation rate
Parasympathetic (cold)
-Decreased sweat production
-Decreased ventilation rate
-Relaxes erector pili
Anatomy and Physiology of Sweating/Sweat Glands
-2-3 million sweat glands
-2 litres of sweat can be lost by evaporation in 1 hr
-Loss of water and electrolytes (Na+)
Thermoregulatory Feedback Loop
Homeostatic system:
-Receptors to measure
-Effectors to alter
-Set point or target value
-Integrating Centre sorts the info from the receptors to send to the effectors eg. Brain
spinal cord
Principles of Feedback
-There needs to be feedback of information from the receptors to allow the current value to
be compared to the set point and implement appropriate actions if they differ
Negative Feedback Loops
-Whenever there is a change in the system, this automatically causes and corrective
mechanism to start
-This reverses the original change
-The bigger the original change the bigger the corrective change
-Carried out by antagonistic effectors
Perturbing factor Stimulus Sensor Integrating centre Effector Response
Vasodilation (arteries/veins/capillaries open and close to hold or release heat)
The Endocrine System
Cushing’s Disease – Hyperadrenocorticism
-Disease of the adrenal cortex excessive amount of gulcocorticoids (cortisol)
Endocrine system
-Part of the regulatory system of the body
-Endocrine means ‘Internal Secretion’
-Endocrine Glands secrete directly into the bloodstream, not through the ducts (Ductless
glands)
Hormones
-Chemical compounds produced in one part of animal body to produce response in
another
-Very small amount can have a large effect on whole organism
-Hormones are secreted by either:
o Endocrine organs OR
o Directly into the bloodstream
-Carried around the bloodstream until they reach their target organs, which are structures
respond to them (they are selective)
Structure of hormones (3 categories):
1. Derived from amino acids Quick Acting
eg. Adrenaline, noradrenalin and thyroid hormones
2. Derived from lipids, belong to one of two groups Slow Acting
Steroid hormones or eicosanoid
eg. Testosterone, oestrogens (steroid), prostaglandin (eicosanoid)
3. Peptide hormones Quick Acting
Formed from peptides or polypeptides
Eg. Antidiuretic hormone (ADH), oxytocin and follicle stimulating hormone (FSH) and
luteinizing hormone (LH)
Effect of hormones
-Each hormone has a specialised effect upon the target cell, tissue or organ
-Alters the function of the target cells
-Can change the properties of the target cell
-Specialised receptor sites on cells
Hormones
-Synthesized, stored and released by non-neural endocrine cells or neurons
-Travel through the circulating blood and exert their effects on target tissues
-Then are metabolically destroyed or excreted from the body
Magnitude of effect depends on:
-Abundance of receptor sites
-Concentration in the blood Balance of rate between synthesis and degradation or
excretion
Hormone secretion
-Released in areas that have a large capillary network
-Either travel freely or with a carrier protein (steroid)
-Release is stimulated by another hormones or a neurotransmitter
-Controlled by a negative feedback mechanism (except oxytocin)
Comparison of Hormonal and Neural Communication
Hormonal Communication
Neural Communication
Chemical
Slower
Rapid
Carried all around body =
widespread
Specific destination = localised
Continue over long period
Short-lived
Unconscious
Mostly conscious actions (pain,
movements)
Major Glands:
-Pituitary
-Thyroid
-Parathyroid
-Thymus
-Adrenal
-Pancreas
-Ovaries
-Testes
-Pineal body
The Hypothalamus
-Integration centre of the body
-Links the endocrine system to the nervous system via the pituitary gland
-Located blow the thalamus, above the brainstem
-Size of an almond (in humans)
-Closely linked (geographically, physically and functionally) with the pituitary gland
-Responsible for certain metabolic processes and some activities of the ANS
-Controls body temperature, hunger, parenting and attachment behaviours, thirst, sleep,
fatigue and circadian rhythms (physical, mental and behavioural changes that follow a 24
hour cycle)
-Synthesizes and secretes neuro-hormones often know as releasing hormones or
hypothalamic hormones stimulate/inhibit pituitary hormone secretion
Relationship between hypothalamus and pituitary gland
-Pituitary gland attached to hypothalamus
-It is also known as the Hypophysis
-Portal system (blood vessels) link hypothalamus to anterior pituitary gland
The Pituitary Gland
-Master endocrine gland
-Size of small pea/bean (humans
-lies within the cranium on ventral surface of midbrain
-Controls the other endocrine glands
Two areas:
-Anterior lobe / adenohypophysis
-Posterior lobe / neurohypophysis
Divided into:
-anterior pituitary (adenohypophysis)
-posterior pituitary (neurophyphysis)
The Anterior Pituitary Hormones
1. Growth Hormone (Somatotropin)
Regulate metabolism of proteins, carbohydrates & lipids within body cells
GH encourage anabolism/synthesis of proteins by body cells
Breakdown lipids for energy production
Discourage cells from using glucose (hyperglycemic effect) effect opposite pancreatic
hormone insulin
2. Prolactin
Triggers & maintains lactation
Due to stimulation of teat nipple
3. Thyroid Stimulating Hormone
Stimulate growth & development of thyroid glands
4. Adrenocorticotropic Hormone
SEE POWERPOINT 4
5. Follicle Stimulating Hormone
Stimulate growth and development of ovaries
Stimulate lining of follicle to secrete oestrogens
6. Luteinizing Hormone
Complete follicle development in ovaries
In males LH (Interstitial cell stimulating hormone) stimulates interstitial cells to develop &
produce testosterone
[interstitial = fluid between the cells]
7. Melanocyte Stimulating Hormone
Control colour changes in the pigment cells (melanocytes)
The Posterior Pituitary
-AKA. Neurohypophysis
-Does not produce any hormone but stores (and releases) two hormones produced by the
hypothalamus
-Vasopressin/Antidiuretic hormone (ADH)
o Increases water absorption by the kidneys
o ADH release is affected by alcohol and caffeine
o Deficiency results to Diabetes insipidus
Polyuria (excessive urination)
Polydipsia (excessive drinking)
-Oxytocin (positive feedback systems)
o Involved in parturition and lactation
o Causes contractions during labour
Glands of the Endocrine System
Thyroid Gland
-Found below the larynx
-Secretes:
o Thyroxine regulates metabolic rate
o Tri-iodothyronine regulates metabolic rate
o Thyrocalcitonin or Calcitonin decreases levels of plasma calcium
-Consists of two lobes located either side of the larynx
-Shape – differs in several animal spp
-Composed of tiny follicles (a sac of pouch like depression or cavity) where thyroid
hormone is produced
-Absorbs material from bloodstream including iodine to produce thyroxine
-2 types of hormone producing cells:
o Follicular cells
o Parafollicular cells (C cells)
Calorigenic effects of thyroid hormones (TH)
Calorigenic: producing or increasing production of heat or energy increasing oxygen
consumption
-Regulate metabolic rate of the body cells – rate at which they burn nutrients to produce
energy (Controls weight gain/loss)
-TH production increases with exposure to cold temperatures
-TH production is inhibited by stress
Follicular Cells
-Hollow secretory cells
-Secretions of thyroxine regulated by TSH (thyroid stimulating hormone) – released by
anterior pituitary gland
Functions:
-Regulate metabolic rate
-Influence absorption of sugars by intestines – how much sugar is absorbed, how much
sugar you need
-Stimulate energy production in cells
-Influences blood – cholesterol levels
Parafollicular Cells
-2nd type of secretory cells in thyroid glands
-Secrete calcitonin
-Regulates Ca2+ levels along with parathyroid hormone
Calcitonin
-Produced by C cells located between the thyroid follicles
-Maintain homeostasis of blood sugar levels
-Body functions:
o Muscle contraction
o Blood clotting
o Milk secretion
o Formation and maintenance of skeleton
-Hypercalcaemic effect – encourages excess Ca to be deposited in the bones
Control of Thyroid Hormones
-Hypothalamus produces the thyrotropin-releasing hormone (TRH)
-TRH stimulates pituitary gland to produce Thyroid stimulating hormone (TSH)
-TSH regulates the rate of T4 and T3 release
-Thyroid hormones are active only if they are free (unbound) in the blood to transport
proteins
Tropins
Hormones that influence the functions of other endocrine glands
Imbalance in thyroid production
-Hypothyroidism – under activity of thyroid gland
-Hyperthyroidism – enlargement of gland and over activity
Hypothyroidism
-Shortage of iodine can result in under secretion of thyroxine
-Can lead to:
o Stunted growth
o Lower resistance to cold
o Lack of energy
Hyperthyroidism
-Over production increases metabolic rate:
o Rapid Heart Rate
o High Blood pressure
o Rapid weight loss
The Parathyroid Glands
-Produces parathormone or parathyroid hormone (PTH)
-Several small pale nodules on or near thyroid gland
-Regulates metabolism and distribution of calcium in blood
o Increases absorption of calcium from digestive tract
o Increases absorption from bone
o Decreases excretion in urine
-4 tiny glands
-Parathyroid Hormone (PTH)
-Metabolism of Ca2+ & P
-Low blood Ca2+ triggers secretion of PTH
-Releases Ca2+ from bones
-Acts of kidneys to ↓ Ca2+ and ↑P excretion
-Promotes Ca2+ absorption from intestine
Hyperparathyroidism
-Overactivity of the parathyroid glands resulting in excess production of PTH
-Harmful to bone
The Adrenal Glands
-Two parts:
o Inner medulla (adrenal medulla)
o Outer cortex (adrenal cortex)
-Both from different embryonic development structures & functions
Medulla
-Produces Adrenalin & Noradrenalin
-Secretion directly controlled by sympathetic nervous system (SNS) stimulated by nervous
impulses in the Brain
-Fight/flight response
Hormones of the Medulla
-Adrenaline/epinephrine
-Noradrenaline/norepinephrine
-‘fight or flight’ hormones
-Not equivalent but similar in action on tissues
-Adrenalin
o Increases heart rate
o Increases blood pressure
o Vasoconstrictors for most tissues
o Vasodilators for muscles and bronchus blood vessels in lungs and muscles increase in
diameter = SA ↑ = ↑ in gaseous exchange = ↑ in efficiency (get more out of each breath)
o Increases blood sugar levels more energy
Fight/Flight
-Frontal lobe of brain is stimulated by nerve impulses
-Hypothalamus & adrenal medulla stimulated
-Adrenal medullary secretion permits a rapid response to stressful stimuli
-Adrenalin causes pupils and bronchioles to dilate, heart rate & blood pressure increases
-Bladder and bowels may evacuate
Noradrenalin
-Also a nerve transmitter substance
-Released at the synapses of sympathetic nerve cells and has the same effect in preparing
a horse for fight or flight
Adrenal Cortex
Produces corticosteroids:
-Cortisone produced in response to stress
-Adrenocorticotropic hormone (ACTH) released from pituitary gland
-Aldosterone – electrolyte and fluid balance
-Glucocorticoids – metabolism of carbs – raising the blood sugar level
-Androgens – sex hormones – responsible for sexual development and function in males
Aldosterone
-Maintains correct mineral balance (electrolytes) – sodium and potassium
-Increases extracellular volume by increasing absorption of sodium from the urine and
colon
Cortisol
-Stress related
-Increases blood sugar level by mobilising energy reserves
-Stimulates protein breakdown
-Inhibits inflammation
Adrenal sex hormones
-Oestrogen in both male and female
-Control body hair growth in human females but levels too low to have substantial effect on
males
-Possibly involved in castrated males trying to mount
Hormones of the Cortex
-Produces more than 24 different hormones
-All steroid-based
-Carried in circulation by carrier proteins
-Corticosteroids – 3 groups
o Mineralocorticoids eg. Aldosterone
o Glucocortoids eg. Cortisol
o Adrenal sex hormones
Diseases of the Adrenal Cortex
-Hypoadrenocorticism
o Addison’s disease adrenal cortices can’t produce adequate levels of aldosterone,
resulting in the increase in retention of potassium in circulation (usually young to middle
age dogs but can occur in any age)
The Pancreas
-Located near duodenum
-Exocrine glandular tissue produces digestive enzymes
-Endocrine tissue produce – Insulin
-Involved in the maintenance of blood sugar levels
-Islet of Langerhans cells produce:
o Glucagon (from alpha cells) increases BSL
o Insulin (from beta cells) decrease BSL
o Somatostatin (from delta cells) suppresses surges of insulin or glucagon production
o Pancreatic peptide (from F cells) related to production of pancreatic enzymes – more
research required (little known about it)
Regulation of blood sugar level
-Glucose conc. Is controlled within the range 0.8 – 1g per dm3 of blood & very < levels
(hypoglycaemia) or very > levels (hyperglycaemia) can be fatal
-Controlled by pancreas
-Glucose receptor cells monitor the concentration of glucose in the blood
-Islets of Langerhans
o α cells glucagon & β-cells - insulin. Antagonistic (works together) and have opposite
effects on blood glucose
o Insulin uptake of glucose by cells for respiration. In the liver – conversion of glucose to
glycogen (glycogenesis). It therefore decreases blood sugar level
o Glucagon breakdown of glycogen to glucose in the liver (glycogenesis) synthesis of
glucose from pyruvate therefore > blood glucose
-After a meal – glucose (G) is absorbed from the gut into the hepatic portal vein, increasing
the blood G concentration
-Pancreas -secretes insulin from its β-cells in response
-Insulin -G to be taken up by the liver and converted to glycogen
-< blood G, which causes the pancreas to stop secreting insulin
-If G level < too far, pancreas detects this & releases glucagon from α-cells
-Glucagon causes the liver to break down some of its glycogen store to G - diffuses into
the blood
-> blood G - causes pancreas to stop producing glucagon
The Gonads
-Male and female gonads = testes & ovaries
-Ovaries
o Oestrogens
Produced in ovary by the developing cells of follicle, prior to ovulation
Increases attractiveness and receptiveness to males
Prepares reproductive tract for fertilisation
o Progesterone
Produced by the corpus luteum of the ovary following ovulation (↑LH)
Maintains pregnancy
o Relaxin
Produced by corpus luteum, placenta and uterus in later stages of pregnancy
Prepares female body for birth
Relaxes ligaments around birth canal
Production is stimulated by LH (early pregnancy) and chorionic gonadotropin (later
pregnancy)
-Testes
o Produces testosterone and oestrogen
o Testosterone
Produced by Cells of Leydig
Involved in sperm production
Maintains secondary sexual characteristics
Maintains sex drive
o Oestrogen
Produced by Serotoli cells
Maturation of spermatozoa
Secretion is controlled by FSH
Introduction to the Central Nervous System
Functions
-Communication system
-Sends rapid electrical and chemical messages around the body to allow mammals an
efficient response to their surroundings
-Help maintain homeostasis by coordinating the function of internal organs
The Brain
-Coordinates body activities
-Made up of approx. 100 billion neurons
-Divided into 3 major parts:
o The cerebrum
o The cerebellum
o The brain stem
Cerebrum
-Largest part of the brain
-Memory is stored
-Movements are controlled
-Impulses from the senses are interpreted
Cerebellum
-Interprets stimuli from eyes, ears, muscles
-Controls voluntary muscle movements
-Maintains muscle tone
-Helps maintain balance
Brain Stem
-Connects brain to spinal cord
- controls involuntary actions
-Made up of:
o The midbrain, the pons act as pathways connecting various parts of the brain with each
other
o The medulla
The Spinal Cord
-Extension of the brain stem
-Bundles of neurons carries impulses from all parts of the body to the brain and from the
brain to all parts of the body
Nerve Cells
Neurons
-Basic functioning units of the nervous system
-Carries messages called an impulse
-Made up of:
o Cell body
o Branches called dendrites and axons
o Dendrites receive messages from other neurons and send them to the cell body
o Axons carry messages away from the cell body
Axons
Take information away from the cell
body
Dendrites
Bring information to the cell
body
Smooth Surface
Rough Surface (dendritic
spines)
Generally only 1 axon per cell
Usually many dendrites per cell
No ribosomes
Have ribosomes
Can have myelin
No myelin insulation
Branch further from the cell body
Branch near the cell body
Types of Neurons:
-Sensory Receive information and send impulses to the brain or spinal cord
-Interneuron send impulses from sensory neurons to motor neurons
-Motor Neuron Conduct impulses from the brain or spinal cord to muscles or glands
throughout the body
Sensory Neuron
Lengt Long dendrites and short
h of
axons
Fibre
s
Locati
on
Cell body and dendrite are outside
of the spinal cord. The cell body is
located in a dorsal root ganglion
Funct Conduct impulses to the
ion
spinal cord
Interneuron
Motor Neuron
Short dendrites and
short or long axon
Short dendrites and long
axons
Entirely within the
spinal cord or GNS
Dendrites and the cell body are
located in the spinal cord. The
axon is outside of the spinal cord
Interconnect the
sensory neuron with
Conduct impulse to an
effector (muscle or
gland)
appropriate motor
neuron
Membrane Potentials
-Intracellular fluid contains
o High concentrations of K+
o Ionized non-diffusible molecules particularly proteins with negatively charged side
chains and phosphate compounds
o Distribution of these charged particles results in the electrical phenomena of plasma
membranes
-Significant role in:
o Signal integration
o Cell-to-cell communication
Electrical Potential
-Aka. Potential Difference
-Units = Volts (or millivolts)
-Movement of electrical charge = Current
-I = V/R
Resting Potential
-In a resting neuron there is a difference in electrical charges of the outside and inside of
the plasma membrane
-Outside = pos+ charge
-Inside = neg— charge
Na+/K+ Pump (electrogenic pump)
-Keeps an ion gradient across the cell membrane
-Three Na+ to the outside of the cell and two K+ ions to the inside
-The sodium-potassium pump is an important contributor to action potential produced by
nerve cells
-Called a P-type ion pump because of ATP interactions phosphorylating the transport
protein (loses a phosphorus which causes a change in its conformation)
Contribution of Active Transport
-Actively transports Na+ molecules out and K+ cells in to ensure there are 3 Na+ outside
and 2 K+ inside
-Occurs via the sodium-potassium pump
Contribution of Facilitated Diffusion
-Sodium-potassium pump creates a concentration and electrical gradient for Na+ and K+
-K+ tends to diffuse out of the cell and Na+ tends to diffuse in Membrane is much more
permeable to K+ (so K+ diffuses out along its concentration gradient)
Gradient Potentials and Action Potentials
-Changes in membrane potential from resting potential produce electrical signals
-Such changes are the most important way nerve cells process and transmit information
Changes in Membrane Potential
-Depolarized when potential less –ve (closer to zero) than resting level (-30mV)
-Overshoot Reversal of the membrane potential polarity = when inside the cell becomes
+ve relative to outside
-Repolarized when a membrane has been depolarised returns to resting value
-Hyperpolarized potential is more –ve than resting level
Action Potential
-Self-regenerating wave of electrochemical activity (in response to stimuli) that allows
excitable cells (nerve/muscle) to carry signal over a distance
-(All or nothing)
-When the cell membranes are stimulated, there is a change in the permeability of the
membrane to sodium ions (Na+) so Na+ ions diffuse into the cell down a concentration
gradient
-The membrane becomes more permeable to Na+ and K+
1. The first step of the action potential is that the Na+ channels open allowing a flood of
sodium ions into the cell. This causes the membrane potential to become positive.
2. At some positive membrane potential the K+ channels open allowing the potassium ions
to flow out of the cell.
Next the Na+ channels close.
This stops inflow of positive charge. But since the K+ channels are still open it allows the
outflow of positive charge so that the membrane potential plunges.
3. When the membrane potential begins reaching its resting state the K+ channels begin to
close.
Now the sodium/potassium pump starts working again and starts transporting sodium out
of the cell, and potassium into the cell so that it is ready for the next action potential.
The action potential travels down the length of the axon as a voltage spike. It does this
using the steps outlined above. As a section of the axon undergoes the above process it
increases the membrane potential of the neighbouring section and causes it to spike. This
is like a mini chain reaction that proceeds down the length of the axon until it reaches the
synapse.
Myelinated Axons
-Axon = a single long, thin extension that sends impulses to another neuron
-Surrounded by a many-layered lipid & the myelin sheath formed by Schwann cells
The Central Nervous System (CNS)
Spinal Cord
Made up of:
o Gray matter – in the centre of the spinal cord and is densely packed with cell bodies and
dendrites
o White Matter – mostly of myelinated axons that carries information from the gray matter
to the brain or other areas of the spinal cord
-Each segment sends sensory information to the brain and receives motor commands
(movements)
Meninges
-Connective tissue layers that surround brain and spinal cord
-Contain blood vessels – nutrients & O2
-Dura mater – outermost
-Arachnoid – delicate & spiderlike
-Pia mater – thin layer
Cerebral Spinal Fluid
-Baths and protects brain and spinal cord
-Circulates between layers of meninges
-May also be involved in autonomic functions like respiration and vomiting
Blood-brain barrier
-Functional barrier separating capillaries in brain from nerve tissue
-Prevents many drugs, proteins and other molecules from passing from blood to brain
-Protects brain from poisons circulating in blood
Synapses
An anatomically specialized junction between two neurons
Point at which the electrical activity in one neurone, the presynaptic neuron, influences the
electrical of metabolic activity in the second, the postsynaptic neuron
Activity at synapses can increase or decrease the likelihood that the postsynaptic neuron
will fire action potentials (by producing a brief, graded potential in the postsynaptic
membrane)
Neurotransmitter
-Chemical messenger used by neurons to communicate with each other or with effectors
eg. Serotonin, dopamine, noradrenaline
In brief:
1. Stored and released by the presynaptic membrane at synapse of first neuron when
stimulated by Action Potential
2. Neurotransmitters diffuse across synapse and bind to postsynaptic receptors on
membrane of second neuron
3. Stimulates or inhibits second-messenger activity within post-synaptic cell
The Peripheral Nervous System (PNS)
Comprised of:
1. Somatic Nervous System
2. Autonomic Nervous System
-Efferent neurons transport signals from the brain to these systems via the efferent division
of the nervous system
-Neuron in the PNS transmit signals between the CNS and the receptors and effects in all
other parts of the body
Somatic Nervous System
-Consists of nerves that:
o Convey sensory information to the CNS
o Transmit messages for motor movement from the CNS to the body
Autonomic nervous system
-Regulates the automatic behaviours of the body (heart rate, blood pressure, respiration,
digestion etc.)
-Innervates (supplies) smooth and cardiac muscle, glands and neurons in the
gastrointestinal tracts
-3 Subsystems
1. Sympathetic Nervous System
2. Parasympathetic Nervous System
3. (Enteric Nervous System) nerve network in the gastro-intestinal tract
Sympathetic Nervous System
Network of nerves that prepares the organs for rigorous activity
-Increases heart rate, blood pressure, respiration etc. (“fight or flight” response)
-Comprised of ganglia on the left and right of the spinal cord
-Mainly uses noradrenaline as a neurotransmitter at the postganglionic synapses
Parasympathetic Nervous System
Facilitates vegetative, nonemergency responses by the organs (“Rest and Digest”)
-Decreases functions increased by the sympathetic nervous system
-Comprised of long preganglion axons extending from the spinal cord and short
postganglionic fibres that attach to the organs themselves
-Dominant during our relaxed states
Enteric Nervous System
-Aka. Intrinsic Nervous System
-One of the main divisions of the nervous systems
-Consists of a mesh-like system of neurons that govern the function of the gastrointestinal
tract
-Usually referred to as separate from the ANS since it has its own independent reflex
activity
PNS Nerves
-Peripheral nerves contain nerve fibres that are the axons of both efferent and afferent
neurons or both
Efferent neurons = transport signals away from the CNS to the effectors Afferent neurons
= transport signals from sensory receptors to the CNS
-43 pairs of nerves
o 12 pairs of cranial nerves
Some only afferent eg. Optic
o 31 pairs that connect with the spinal cord as spinal nerves
Both afferent and efferent
Spinal Nerves
-31 pairs
-Categories for each of the pairs of spinal nerves
-8 cervical spinal nerves
-12 thoracic spinal nerves
-5 lumbar spinal nerves
-5 sacral spinal nerves
-1 coccygeal spinal nerve
Reflexes and the reflex arc
Reflexes Rapid, automatic response to stimuli designed to protect the body and maintain
homeostasis
-Maintain balance and posture (eg. Spinal reflexes control trunk and limb muscle)
-Brain reflexes involve reflex centre in brainstem (eg. Eye movement)
-Somatic Reflexes involve contraction of skeletal muscles
-Autonomic reflexes regulate smooth muscle, cardiac muscle and endocrine glands
-All reflexes have basic structure called a reflex arc
Reflex Arc
-Originate from a sensory receptor – detect changes in internal/external environment
-Reflex arc – a response to a perturbing stimulus that acts to return the body to
homeostasis
-Action Potential ( nerve impulse) go through sensory neurons to gray matter of spinal cord
to brain
Classification
Sensory Receptors are classified by 3 methods:
1. Receptor complexity
2. Classification by location
3. Classification by stimulus detected
Parts of the Reflex arc
1. Receptor
-detects the stimulus and sensitive to a specific type of internal or external change
2. Sensory Neuron
-conveys the sensory info to brain or spinal cord
-Transmit nerve impulses from the receptor into the brain or spinal cord
3. Interneuron (relay neurons)
-Serves as processing centre, conducts nerve impulses from the sensory neuron to a
motor neuron
4. Motor Neuron
-Transmits nerve impulse from the brain or spinal cord out to an effector (muscle or
endocrine gland)
Monosynaptic Reflex
A two neuron reflex arc
-Involve only a sensory neuron & motor neuron – no interneuron
-Only one synapse between them
-Relies on a specialised structure within the muscle (muscle spindle)
Stretch Reflex
-Stretching the muscle activates the muscle spindle
-Excited motor neurons of the spindle cause the stretched muscle to contract
-Afferent impulses from the spindle result in inhibition of the antagonist
-Example: Patellar Reflex
o Tapping the patellar tendon stretches the quadriceps and starts the reflex action
o The quadriceps contract and the antagonistic hamstring relax
Stretch Reflex
Monosynaptic Stretch Reflex
-Simplest reflex because it only has one synapse in the path of its arc
-Muscles spindles contain the sensory receptors for the stretch reflex
-Each spindle contains modified muscle fibers called spindle of intrafusal fibers (inside
spindle), innervated by efferent fibers
-The middle segment of each spindle fiber acts as a mechanical stretch receptor that is
connected to a sensory afferent nerve to the spinal cord
-Stretching of the muscle stretches the spindle fibers activating the muscle spindle stretch
receptors and the associated sensory fibers
Afferent = Sensory Efferent = Motor