Nervous System Notes
Organization of the Nervous System
Central nervous system (CNS)= brain and spinal cord
-integrating and command center
- Peripheral nervous system (PNS)= all nerves outside the CNS
Neuron (nerve cell)= specialized to transmit message
 Dendrites= structures that receive incoming messages, has receptors for
neurotransmitters, conducts electrical signal towards cell body
 Cell body= structure that integrates and processes messages
 Axon=structure that carries electrical signal away from the cell body
 Axon terminals= at the end of the axon, releases neurotransmitters
 Myelin sheath=insulation found along axon of neuron, allows for electrical
impulse to travel faster
Neuroglia-support cells
In CNS
 Astrocytes- maintain the blood brain barrier, absorb/recycle neurotransmitters
 Microglia- phagocytis cells that remove waste
 Ependymal cells- help form and circulate cerebrospinal fluid
 Oligodendrocytes-stabilize neuron and form myelin that wraps around axon
In PNS
 Schwann cells- make myelin sheaths
 Satellite cells-surround cell body and regulate environment around neuron)
Action Potential= propagated changes in the membrane potential that affect the entire
excitable membrane
 Action potentials allow long-range communication between cell body and
axon terminals
 Axon potentials travel dendrite to cell body to axon
Synapse= where a neuron communicates with another cell to pass along message
 When action potential travels down axon it will cause neurotransmitters to be
released from (from pre-synaptic cell) into synaptic cleft
 Post synaptic cell has receptors for neurotransmitters, neurotransmitters will
attach to receptor causing an electrical impulse
Spinal Cord- extension of brainstem and begins at foramen magnum through vertebral
canal at L1, L2-S5 spinal roots form cauda equina
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Protection and coverings
o Vertebral column- the spinal cord is in a canal formed by the vertebral
foramina
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Meninges (spinal meninges), cover cord and spinal nerves until they exit
vertebral column
o Dura mater—outermost layer, contains epidural space
o Arachnoid mater—middle layer, contains subarachnoid space which
contains CSF
o Pia mater—innermost layer
o Filum terminale supports provides longitudinal support for spinal cord
o Extended thickened portions of pia mater called denticulate ligaments hold
spinal cord in place laterally
Internal anatomy
o White matter-outer region, myelinated & unmyelinated axons
o Grey matter-inner region, forms butterfly shape, mostly neuron cell bodies,
neuroglia, unmyelinated axons
o Central canal-contains cerebrospinal fluid
Spinal nerves= carry electrical signals to and from the spinal cord, 31 pairs spinal
nerves
 Spinal nerves are mixed meaning they carry both sensory and motor information,
form from anterior and poster roots
 Anterior root contains axons of motor neurons
 Posterior root contains axons of sensory neurons
 Posterior root ganglion (spinal ganglion) contains cell bodies of
sensory neurons in posterior root
Two main functional divisions
1. sensory (afferent) division- carries signals toward CNS, from skin, muscles and
joints (somatic), and from visceral organs
2. motor (efferent) division- carries signals away from CNS to effector organs
 somatic division: to skeletal muscle, voluntary control
 autonomic division: to smooth and cardiac muscle, glands; involuntary
control, further divided into sympathetic division ("fight or flight") and
parasympathetic division ("resting and digesting")
Plexuses- the ventral rami of all the spinal nerves (except thoracic) branch into
networks
Cervical plexus (from C1-C4)
1) mostly serves skin and muscles of head, neck, shoulders, upper chest
2) phrenic nerve serves diaphragm (for breathing)
Brachial plexus (from C5-T1)
1) serves upper limbs
Lumbar plexus(fromL1-L4)
1) serves abdomen, lower limbs
Sacral plexus (from L4-S4)
1) serves lower limbs
2) contains sciatic nerve
Reflex= rapid, predictable motor response to a stimulus. Many are unlearned and
involuntary
 Spinal reflexes are unlearned and involuntary
a. integrating center is the spinal cord
b. no brain involvement necessary, but brain is informed of what happened
Reflex arc
1. Receptor - receives stimulus
2. sensory neuron - electrical signal travels to...
3. integrating center - the part of the CNS that decides on response, brain stem or
spinal cord for unlearned reflexes
4. motor neuron - signal sent to...
5. effector - the part of the body that responds (skeletal muscle or gland)
Major Parts of the Brain
Brain covered by meninges that are continuous with spinal meninges
Cerebrum
Paired lobes (frontal, parietal, temporal, occipital)
 Frontal- allows for problem solving, planning, concentration, initiates muscle
movement
 Parietal- interprets speech, sounds, and general sensations
 Temporal-controls visual and auditory memory and controls basic hearing
mechanisms
 Occipital- processes visual information
Made up of outer gray matter (cortex) and inner white matter
Gray matter (cortex)
1. allows us to perceive, understand, communicate, remember, do voluntary
movements(skeletal muscle)
2. divided into many functional areas
1) motor cortex- control voluntary motor function (skeletal muscle)
2) sensory cortex- receives sensory information from receptors( touch, temp,
pain, vibration, pressure)
3) auditory cortex- hearing
4) visual cortex- vision
5) gustatory- taste
6) olfactory- smell
3. each hemisphere specializes in functions on the opposite side of the body
(contralateral)
4. hemispheres not equal in function
1) left side generally more involved in logical, analytical tasks like language and
math
2) right side generally more involved in spatial perception, art, music
Diencephalon
 thalamus-preliminary processing of sensory input - screens out unimportant
stimuli and passes on significant input to the appropriate area of cortex
 hypothalamus- controls emotions, autonomic function, controls body
temperature, regulates metabolism, sleep, and fluid/ion levels, hormone
production
Brain stem- connects brain to rest of body
1. Midbrain- processes visual and auditory information and controls reflexes visual
reflexes (eyes tracking an object, turning towards a loud noise)
2. pons-connects cerebellum/brainstem, sensory and motor tracks, respiratory reflex
3. medulla oblongata –regulate autonomic functions such as heart rate, blood pressure
Cerebellum- coordinates movements
Cranial Nerves
- Mnemonic device- Oh, Oh, Oh, To Touch And Feel Very Good Velvet, AH
1 I OLFACTORY
2 II OPTIC
3 III OCULOMOTOR
4 IV TROCHLEAR
5 V TRIGEMINAL
6 VI ABDUCENS
7 VII FACIAL
8 VIII VESTIBULOCOCHLEAR
9 IX GLOSSOPHARYNGEAL
10 X VAGUS
11 XI ACCESSORY
12 XII HYPOGLOSSAL
Sensation: conscious or subconscious awareness of internal or external stimuli
Perception: conscious awareness and interpretation of sensation
Components of sensation
1. stimulus- a change in the environment capable of activating sensory neurons
2. transduction- sensory receptor or sense organ transduces stimulus into a nerve
impulse
3. conduction- nerve impulse conducted to CNS by afferent fibers
4. translation- CNS receives and interprets information
General senses: touch,pressure,vibration,temperature,pain
Sensory Receptors
 mechanoreceptors-sense mechanical pressure or stretching
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touch, pressure, vibration, proprioception, hearing, blood pressure
thermoreceptors- sense temperature
chemoreceptors- sense chemicals
taste, smell, changes in body fluids
nociceptors-sense pain
Special Senses: only found in certain place in the body
Olfaction (smell), gustation (taste), vision, equilibrium (balance), hearing
Olfaction- smell is the binding of organic molecules to receptors deep in the nose
 Your nose is lined with olfactory receptors
• Air flows in carrying organic molecules
• Organic molecules dissolve in mucus lining
• Organic molecules bind to receptors
• Impulse sent through Olfactory Nerve
Gustation-provides information about the foods and liquids consumed
 Tongue covered in lingual papillae that contain taste buds.
 Taste buds = sensory structures with taste receptors that respond to various
chemical stimuli, and specialized epithelial cells.
 Taste receptors (or gustatory receptors) are distributed on tongue and portions
of pharynx and larynx, located in taste buds
Types of lingual papillae:
 Filiform papillae: only one that does not contain taste buds, provide friction
 Fungiform papillae
 Circumvallate papillae
 Foliate
Primary taste sensations: sweet, salty, sour, bitter, Umami
Vision-receptors located in retina of eye
External eye structures-protection
 Eyelid: help to protect the eye from abrasions by blocking particles that may land
on the surface of the eye
 Conjunctiva: thin membrane on inner surface of each lid, extends over the white
areas of the eye (the sclera)
 Lacrimal gland: produce tears
Three Layers of the Eye
1. Outer fibrous tunic
 Sclera (white of eye): tough white tunic
 Cornea: outer, transparent structure at the front of the eye, it is the eye's
primary light-focusing structure.
2. Middle vascular tunic
 Iris: colored part of eye, central aperture pupil, controls the size of the pupi
o Pupil = opening in center of iris, allows light to enter the eye
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Choroid: thin pigmented and highly vascular layer, firmly attached to the retina
and provides nourishment to retina
 Ciliary body: between the choroid and the iris, provides attachment for the lens.
o Ciliary muscle: controls accommodation (bending lens)
o Ciliary process: contributes in formation of aqueous humor
 Lens: posterior to cornea, helps focus and refract light to retina
3. Inner neural tunic (Retina)
 Contains visual receptors (photoreceptors) and associated neurons
Two types of photoreceptors:
 Rods: highly sensitive; allow vision in very dim light, No color discrimination:
provide black-and-white vision only
 Cones: Color vision, sharper, clearer images, require more intense light
Vision
 Light must pass through onto retina
 Light causes rods and cones to change membrane potential and signals
travel with optic nerve
Hearing and Equilibrium-located in the internal ear
External ear
1. auricle (a.k.a. pinna)-elastic cartilage covered with skin, directs sound into ear
2. external auditory canal (meatus)-passageway for soundwaves to travel to eardrum
Middle ear
1. Tympanic membrane (eardrum) = thin, semitransparent sheet that separates external
ear and middle ear, vibrates when hit by sound waves, transferring vibrations to the
bones of the middle ear
2. Ossicles are the bones that transmit vibration to the inner ear
-malleus, incus, stapes
Inner ear
-Contains sensory organs for hearing and equilibrium, receives amplified sound waves
from middle ear
Bony labyrinth-layers of bony chambers, filled with fluid (perilymph) that conducts
vibrations
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Three parts: Semicircular canals, Vestibule, Cochlea
Membranous labyrinth-fluid filled tubes inside bony labyrinth, Houses receptors for
hearing and equilibrium, made up of semicircular ducts, utricle and saccule, and
cochlear duct
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Semicircular ducts (within semicircular canals)- Receptors stimulated by rotation
of head
Utricle and saccule- Provide sensations of gravity and linear acceleration
Cochlear duct (within cochlea)- Receptors stimulated by sound
Hearing
1.when sound waves strike the tympanic membrane vibration is transmitted through the
ossicles to the fluid in the cochlea
2.the structures inside vibrate and hair cells are stimulated, resulting in nerve impulses
being sent along the vestibulocochlear nerve to primary auditory cortex on the temporal
lobe