Human Anatomy & Physiology
Nervous Tissue, Brain, & Spinal Reflex
1999
SOHI
B.Rife
page 1 / 6
Homeostasis - is a condition in which the body’s internal environment remains within certain physiological limits. For the
body’s cells to survive, the composition of the surrounding fluids must be precisely maintained at all times.
Negative feedback system - The reaction of the body (output) counteracts the stress (input) in order to restore homeostasis.
(negative because output opposite of input)
example - Increase blood glucose --> ß cells (pancreas) --> insulin --> increase glucose uptake by cells --> lowers blood
sugar --> balance
Positive feedback system - The output intensifies the input. This system is therefore a stimulatory- stimulatory one.
(magnifies the initial effect.
example - onset of labor fetus head pushes against uterus --> neuroendocrine reflex --> signal for posterior pituitary to
release oxytocin --> stimulates uterine contractions
Basic Principles of Electricity
1. Exchange and sharing of neg. charged electrons between atoms to form ions or bonds.
2. Most chem. reactions result in neutral molecules w/ equal numbers of electrons (e -) and protons +, but in some cases ions
are formed having an electric charge (positive due to missing e - or negative due to additional e-.)
3. For example: extracellular fluid has high Na + and Clintracellular fluid has high K + and RPO44. Fundamental principles of electricity: like charges repel, unlike charges attract when a (+) moves toward a (-),
“work” is done (W = F x d)
Nervous Tissue
Organization
Central Nervous system (CNS) - is the control center for the entire nervous system and consists of the brain and spinal cord.
Peripheral Nervous system (PNS) - various nerve processes outside the CNS.
Afferent system - consists of nerve cells that convey information from receptors in the periphery of the body to the
central nervous system. (sensory neurons)
Efferent system - consists of nerve cells that convey information from the CNS to muscles and glands.(motor
neurons)
Somatic Nervous system (SNS) - consist of efferent neurons that conduct impulses from the CNS to
skeletal muscle tissue. (motor neuron)
Autonomic Nervous system (ANS) - consist of efferent neurons that conduct impulses from the CNS to
smooth muscle tissue, cardiac muscle tissue and glands.
Sympathetic Nervous system - serves as the emergency or stress ststem, controlling visceral
effectors during strenous exercise and strong emotions: anger, fear, hate, or anxiety.
(shark = sympathetic)
Parasympathetic Nervous system - control of many visceral effectors under normal,
everyday conditions
Histology (Nerve Tissue)
Gray Matter - nerve tissue comprising cell bodies and unmyelinated axons and dendrites.
White Matter - nerve tissue that is myelinated, covered with white myelin.
Nerve - A bundle of fibers located outside the central nervous system.
Ganglia (ganglion sing.) - A swelling located on a nerve that results from the aggregation of the nerve cell bodies located
within the PNS.
Nucleus(i) - a mass of nerve cell bodies located within the CNS
Neuroglia - are the cells of the nervous system that perform the functions of support and protection.
Astrocytes - are star-shaped cells found in the CNS that serve to support the function of the neuronal cells. Astrocytes may
be involved in myelin formation, transport of nutrient materials, and the maintenance of the interstitial fluid and
gas exchange (blood-brain barrier).
Human Anatomy & Physiology
Nervous Tissue, Brain, & Spinal Reflex
1999
SOHI
B.Rife
page 2 / 6
Oligodentrocytes - Nonneuronnal cells with long extensions which form myelin sheaths around axons of myelinated neurons
within the CNS.
Microglia - Cells that engulf and destroy microbes and cellular debris; function as small macrophages.
Ependyma - form a epithelial lining for the ventricles of the brain and play a role in CSF secretion.
Neurons - are the basic information-processing units of the nervous system.
There are ~ 12 billion in the brain.
Neurons
Specialized cell type: 1. distinctive cell shape
2. outer membrane capable of generating nerve impulse
3. special feature is the synapse (involved in interneuron communication.)
4. loss of mitotic division capacity
Basic Anatomy of Neuron
Cell body (peridaryon) - contains a well-defined nucleus surrounded by a granular cytoplasm.
Nissl bodies - orderly arrangements of granular (rough) ER and free ribosomes in the cell body of a neuron.
Dendrites - thick extensions of the cell body; their function is to conduct nerve impulses toward the cell body.
Initial segment (Axon hillock) - beginning portion of an axon plus the region of cell body that gives rise to the axon.
Axon - relatively long process of a neuron that conducts impulses away from the cell body.
Telodentria - name of fine filaments formed by final branching of an axon.
Synaptic end bulbs - expanded terminal process of the axon which stores and releases neurotransmitter.
Schwann Cell (neurolemmocytes) - Name of cell type which forms myelin sheaths around axons outside the CNS.
Myelin Sheath (neurolemma) - multiple wrappings of insulative, lipid membrane around axons in white matter.
Nodes of Ranvier (neruofibral nodes) - unmyelinated gaps between segments of myelin sheaths along an axon.
Classification of Neurons
Multipolar - structural type of neuron having several dendrites and one axon coming off the cell body
(motor or efferent neurons are structurally this type). Most neurons of the brain and spinal cord.
Bipolar neurons - have one dendrite and one axon and are found in the retina of the eye, inner ear, and olfactory area.
Unipolar (pseudounipolar neurons) - Structural type of neuron that appears to have only one process extending form the
cell body; functions as a sensory neuron. (Figure 12-5 pg 338)
Sensory (afferent) neurons carry nerve impulses (AP) toward CNS
Motor (efferent) neurons carry nerve impulses away from CNS
Association (interneuron) neurons - carry impulses from sensory neurons to motor neurons and are located in the brain and
spinal cord
(~ 90% of all neurons)
Physiology (nonmyelinated neurons)
Resting Membrane Potential (RMP) is -70 mV. Membrane potential (voltage) is the measure of the difference between
the elec. charge inside vs outside; it is due to unequal concentrations of K + Na + and RPO4-3 . Membrane is
polarized.
Outside
(14x) Na +
Result (+)
3 Na + out
------------------------------------------------------------------------------------ pump
Inside
(30x) K+ (Mega) RPO4-3 Result (-)
2 K + in
Sodium-potasium pump - requires energy from ATP (cleaved)
Membrane permeability to K + is 100 times greater than that to Na + .
Human Anatomy & Physiology
Nervous Tissue, Brain, & Spinal Reflex
1999
SOHI
B.Rife
page 3 / 6
Action Potential (AP) (essay question)
1. A stimulus is any condition in the environment capable of altering the resting membrane potential. Sufficient stimulus to
initiate and AP is called a threshold stimulus.
2. Depolarization occurs due to increased Na + permeability.
3. Voltage-sensitive Na + gates open (positive feedback) increasing depolarization.
Action Potential (AP) cont.
4. Membrane depolarization increase to +30 mV. (AP is - 70 mV --> + 30 mV)
5. Repolarization occurs due to Na + gates closing and K + gates opening. (Homeostasis)
6. Hyperpolarzation (excess negative occurs due to K + out and Cl- in.
7. After AP pass, net inc. of Na + remains --> activates Na + K + ion pump to return to RMP.
8. Moving Action Potential due to local current.
Refractory period - refers to the period of time during which a second action potential cannot be initiated.
(absolute - no stimulus, relative - strong stimulus).
Saltatory Conduction - is a process by which nerve impulse rapidly jumps from node of Ranvier to node of Ranvier
along a myelinated neuron.
Conduction or Transmission across a Synapse
Synapse - a junction between two neurons.
Electrical synapses - nerve impulse passes through gap junctions.
Chemical synapses - neuron secretes a chemical substance called a neurotransmitter that acts on receptors of the next
neuron.
A synapse has three components: a Presynaptic Membrane, a Synaptic Cleft - a space ~ 20 nm across filled with
extracellular fluid, and a Postsynaptic Membrane.
Neurotransmitter - is a chemical messenger; each neuron makes only one type. Cholinergic neurons release acetylcholine
(ACh). Adrenergic neurons release norepinephrine (NE).
Acetylcholine (ACh) excites skeletal muscles, inhibits cardiac muscles
Norepinephrine (NE) excites cardiac muscles, inc. heart rate
Synaptic Cleft - a space ~ 20 nm across filled with extracellular fluid.
Synapse Events (essay question)
1. Arrival of nerve impulse (AP) inc. Ca+ permeability in end bulb of presynaptic neuron.
2. Release of neurotransmitter (NT) into synaptic cleft.
3. Binding of NT to receptor in membrane of postsynaptic neuron.
4A. If excitatory NT binding (EPSP), inc. Na+ permeability in postsynaptic neuron.
One NT = depolarization 0.5 mV , need 15 mV for threshold AP thus need 30 -40 NT for AP.
4B. If inhibitory NT binding (IPSP), inc. Cl- in and/or K+ out --> hyperpolarization (inc neg.) no AP.
Human Anatomy & Physiology
Nervous Tissue, Brain, & Spinal Reflex
1999
SOHI
B.Rife
page 4 / 6
Postsynaptic neuron may be impinged by up to 103 presynaptic end bulbs.
Spatial summation - When stimuli from different sources arrive simultaneously but at different sites on the same neuron,
their effects can be algebraically summed and initiate an AP.
Temperoral summation - The increased effect on the excitability of a nerve cell membrane caused by stimuli form a
particular presynaptic terminal arriving in rapid succession resulting in an AP.
Anatomy & Physiology Lecture BIO 207
The Brain and the Cranial Nerves
I
Brain
II.
Cerebrospinal Fluid (CSF)
III.
Blood Supply / Neurotransmitters
I. Brain
A. Principle Parts of the brain are:
1. brain stem
2. diencephalon
3. cerebrum
4. cerebellum
B. Brain Stem - is the expanded portion of the spinal cord as it approaches the cerebrum.
1. Medulla Oblongata - is continuous with the upper part of the spinal cord.
It contains nuclei that are reflex centers for:
a. regulation of heart rate
b. respiration rate
c. vasconstriction
d. swallowing
e. coughing
f. vomiting
g. sneezing
h. hiccuping
2. Pons - is located superior to the medulla. (See Fig. 14-1, 14-3)
a. It connects the spinal cord with the brain and links parts of the brain with one another by way of tracts.
b. It relays impulses from the cerebral cortex to the cerebellum related to voluntaryskeletal movements.
c. The reticular formation of the pons contains the pneumotaxic and apneustic areas,
which help control respiration
d. It contains the nuclei for cranial nerves V - VIII.
3. Midbrain - connects the pons and diencephalon.
a. It conveys motor impulses from the cerebrum to the cerebellum and spinal cord
b. sends sensory impulses from spinal cord to thalamus
c. regulates auditory and visual reflexes
C. Diencephalon - consists primarily of the thalamus and hypothalamus.
1. Thalamus - is located superior to the midbrain
a. contains nuclei that serve as relay stations for all sensory impulses except smell.
b. It also registers conscious recognition of pain and temperature and some awareness of touch & pressure.
c. It also contains nuclei that are centers for synapse in the somatic motor system, such as voluntary
motor action
and arousal.
2. Hypothalamus is found inferior to the thalamus. The chief functions include:
a. It controls and integrates the autonomic nervous system, which regulates contraction of smooth
muscle,
cardiac muscle, and secretions of many glands.
b. It is involved in the reception and integration of sensory impulses from the viscera.
c. It is the principal intermediary between the nervous system and the endocrine system.
When the hypothalamus detects certain changes in the body, it releases a variety of hormones.
d. It coordinates mind-over-body phenomena.
e. It is associated with feelings of rage and aggression.
f. It controls normal body temperature.
g. It regulates food intake (hunger & satiety centers)
h. It contains a thirst center to regulate fluid intake.
Human Anatomy & Physiology
Nervous Tissue, Brain, & Spinal Reflex
1999
SOHI
B.Rife
page 5 / 6
D. Cerebrum - is the largest part of the brain. It surface (cortex) contains gyri, fissures, & sulci.
1. Anatomy:
a. The cerebrum is nearly separate into right and left halve, called hemispheres, by the
longitudinal fissure.
Internally it remains connected by the corpus callosum.
b. Each cerebral hemisphere is further subdivided into four lobes named the frontal, parietal, temporal,
and occipital
c. Mapping
2. Functions
a. The sensory areas of the cerebral cortex are concerned with the interpretation of sensory impulses.
b. The motor areas are the regions that govern muscular movement.
c. The association areas are concerned with emotional and intellectual processes
3. Electroencephalogram (EEG)
a. Brain waves generated by the cerebral cortex are recorded as an electroencephalogram (EEG)
b. It may be used to diagnose epilepsy, infections, tumors, trauma, and brain death.
4. Brain Lateralization
a. Recent research indicates that the two hemispheres of the brain are not bilaterally symmetrical, either
anatomically or
functionally.
b. The left hemisphere is more important for right-handed control, spoken and written
language, numerical and scientific skills and reasoning.
c. The right hemisphere is more important for lift-handed control, musical and artistic
awareness, space and pattern perception, insight , imagination, and generating
images of sight, sound, touch, taste, and smell.
E. Cerebellum - occupies the inferior and posterior aspects of the cranial cavity.
Functions: In the coordination of skeletal muscles and the maintenance of normal muscle tone
and body equilibrium (walking)
II.
Cerebrospinal Fluid (CSF)
A. Ventricles - are cavities in the brain that communicate with each other, with the central canal of the
spinal cord, and with the subarachnoid space.
B. Cerebrospinal Fluid (CSF) - is formed primarily by filtration from networks of capillaries called choroid
plexuses, found in the ventricles, and circulates through the ventricles, the central canal, and
subarachnoid space.
1. Absorption by the arachnoid villi occurs at the same rate at which CSF is produced in the
choroid plexuses, thereby maintaining a relatively constant CSF volume and pressure.
2. CSF protects by serving as a shock absorber and the brain is “buoyed”in it. It also delivers
nutritive substances from the blood and removes wastes. It also is an ideal bathing
medium for neuro tissue.
3. If CFS cannot circulate or drain properly, a condition called hydrocephalus develops.
III.
Blood Supply / Neurotransmitters
A. Blood Supply
1. The blood supply to the brain is via the cerebral arterial circle.
2. Although the brain composes only about 2% of the total body weight, it utilizes about 20 % of
the oxygen used by the entire body. The brain is one of the most metabolically active
organs of the body, and the amount of oxygen it uses varies with the degree of mental activity.
3. Any interruption of the oxygen supply to the brain can result in weakening, permanent
damage, or death of brain cells.
4. Carbohydrate storage in the brain is limited, so the supply of glucose to the brain must be continuous.
Glucose deficiency may produce mental confusion, dizziness, convulsions, and unconsciousness.
B. Blood Brain Barrier (BBB)
1. is a concept that explains the differential rates of passage of certain material from the blood
into the brain
a. glucose, salt ions, H2O, CO2, and O2 can cross freely
b. proteins, many drugs, molecules of molecular wts. >2000 can not cross freely.
2. The BBB functions as a selective barrier to protect brain cells from harmful substances.
Human Anatomy & Physiology
Nervous Tissue, Brain, & Spinal Reflex
1999
SOHI
B.Rife
page 6 / 6
3. An injury to the brain due to trauma, inflammation, or toxins (drugs) causes a breakdown of
the BBB, permitting the passage of normally restricted substances into the brain tissue.
C. Neurotransmitters in the Brain
1. Examples of neurotransmitters (NT) include acetylchloine (ACh), norepinephrine (NE),
dopamine (DA) and glycine.
2. Neuropeptides are another group of NT. Many of these act as natural painkillers in the body
including enkephalins, endorphins, and dynorphin.
3. Other neuropeptides serve as hormones or other regulators of physiological responses.
The Spinal Cord and the Spinal Nerves
I
Terms
II.
Spinal Cord - Structure & Function
III.
Reflex Arcs
I. Terms
White matter - Those parts of the CNS that appear white. Made up mostly of myelinated nerve fibers.
Gray matter - That part of the CNS that has a gray color in its natural state. Microscopically, it consists mainly of cell
bodies and the unmyelinated parts of nerve cells.
Nerve - A bundle of fibers located outside the nervous system.
Ganglia - A swelling located on a nerve that results from the aggregation of the nerve cell bodies located outside the CNS.
Nucleus (ei) - A mass of nerve cell bodies and dendrites in the CNS.
Tracts - A bundle of myelinated fibers of similar function in the CNS .
III. Reflex Arc (essay question)
A. Basic Components
1. Receptor - Dendrite that responds to a specific change in the internal or external environment by initiating a nerve
impulse.
2. Sensory neuron - Passes the nerve impulse form the receptor to its axonal termination in the CNS.
3. Center (Synapse) - A region in the CNS where an incoming sensory impulse generates an outgoing motor impulse.
Usually contains one or more association neurons between sensory and motor neurons.
4. Motor neuron - Transmits the impulse to the effector organ of the body that will respond, such as a muscle or a gland.
5. Effector - The organ of the body that responds to the motor nerve impulse.
B. Definitions
1. A reflex arc is the shortest route that can be taken by an impulse from a receptor to an effector.
2. A reflex is a quick, involuntary response to a stimulus that passes along a reflex arc. Reflexes represent the body’s
principal
mechanisms for responding to certain changes (stimuli) in the internal and external environment
C. Somatic spinal reflexes
1. Include: the stretch reflex, tendon reflex, flexor reflex, and crossed extensor reflex
2. Monosynaptic reflex arc
a. contains one sensory and one motor neuron
b. a stretch reflex such as the patellar reflex is an example
c. patellar reflex - knee jerk - involves extension of the lower leg by contraction of the
quadriceps femoris muscle in response to tapping the patellar ligament. Reflex blocked by
damaged afferent or efferent nerves to muscle or reflex centers of 2-3-4 lumbar segments in spinal cord.
3. Polysynaptic reflex
a. contains a sensory, association, and motor neuron.
b. the tendon reflex is an example.