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VETT 230 ~ Veterinary Anatomy & Physiology III
Wk 8 ~ The Nervous System
71
Veterinary Medicine
Not Applicable
07/30/2013

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Term
Neuroglial cells
Definition
glial cells
- provide structural and functional support and protection to neurons
- outnumber neurons 10:1 but not directly involved in transmission of info or impulses through the nervous system
- rather they are important parts of the infrastructure necessary for the neurons to do their job
Term
Neuron
Definition
- basic, functional units of the nervous system
- the smallest pieces of the system that show basic nervous system functions, such as responding to stimuli and conducting impulses from one part of the cell to another
- high maint
- high requirement for o2, can’t live w/o for long
- that’s why CPR must be started w/in a few min of cardiac arrest – heart may start beating again after that but could be brain damage if neurons w/o O2 for long
- shortly after animal born, its neurons lose their ability to repro but they can regen cell processes if the vcell body remains intact
- this lack of repro ability is why serious nervous system, such as strokes and spinal cord damage, are often so debilitating and have such long-term effects
Term
Neuron structure
Definition
- central cell body (soma or perikaryon)
- cell processes
 dendrites – receive stimuli
 axons – conducts nerve impulses away
Term
Dendrites
Definition
- receive stimuli from other neurons and conduct the stimuli to the cell body
- may serve as sensory receptors for heat, cold, touch, pressure, stretch, or other physical changes from inside or outside the body
- short, numerous and multibranched
Term
Axons
Definition
- conduct nerve impulse away from cell toward another neuron or an effector cell
- single, long process; may be covered with myelin
- white matter; tissue containing myelinated axons
- myelinated axons conduct impulses faster than unmyelinated one
- myelin sheath; cell memb of glial cells tightly wrapped around the axon
 oligodendrocytes in the brain and spinal cord
 schwann cells in the nerves outside the brain and spinal cord
- mult Schwann cells or oligodendrocytes cover the entire length of the axon
- nodes of Ranvier; gaps between adjacent glial cells
Term
Sodium-potassium pump
Definition
- specialized molecule that helps maintain cell resting state
- Pumps (Na+) from inside of neuron to the outside
- pump (K+) from outside of neuron to inside
Term
Depolarization
Definition
- neuron receives external stimuli
- sodium channel opens on neuron cell membrane
- sodium ions flow into cell by passive diffusion
- Action potential
 during depolarization, inside of the neuron goes from a negatively charged resting membrane potential to a net positive charge due to inflow of sodium ions
 creates large change in electrical charge from negative to positive
Term
Repolarization
Definition
- sodium channels close
- K+ channels
- K+ diffuses out of cell
- resting state restored
Term
Central Nervous System (CNS)
Definition
- brain and spinal cord
- one of two main divisions of the nervous system
Term
Peripheral Nervous System (PNS)
Definition
- cordlike nerves that link the CNS with the rest of body
- extends 0utward from the central axis toward the periphery of the body
- cranial nerves originate directly from the brain
- spinal nerves emerge from the spinal cord
Term
Afferent Nerves
Definition
- conduct nerve impulses toward the CNS
- also called sensory nerves – conduct sensations from sensory receptors in the skin and other locations in the body to the CNS
Term
Efferent Nerves
Definition
- conduct nerve impulses away from the CNS
- also called motor nerves – cause skeletal muscle contraction and movement
Term
Autonomic Nervous System
Definition
- controls and coordinates autonomic fxns
- ex: slowing of the HR in response to increased BP
Term
Somatic Nervous System
Definition
- actions under conscious or voluntary control
Term
Threshold Stimulus
Definition
- stimulus must be sufficient to make the neuron respond and cause complete depolarization
- “all or nothing principle” – neuron depolarizes to its max strength or not at all
- conduction of the action potential – spreading wave of opening sodium channels in sufficient numbers to allow sodium influx and depolarization – wave of depolarization or nerve impulse
Term
Refractory Period
Definition
- time period during which a neuron is insensitive to add’l stimuli – cell is still in depol/early repol
- absolute refractory period – during sodium influx and early potassium outflow
- relative refractory period – during end of the repol period
 may be poss to stim another depol if stim is very lg
Term
Synapse
Definition
junction between two neurons or a neuron and a target cell
Term
synaptic cleft
Definition
gap between adjacent neurons
Term
presynaptic neuron
Definition
neuron bringing the depolarization wave to the synapse (releases neurotransmitter)
Term
postsynaptic neuron
Definition
contains receptors for the neurotransmitter
Term
Saltatory Conduction
Definition
- rapid means of conducting an action potential
- depol in myelinated axons can only take place at the nodes of Ranvier
Term
telodendron
Definition
branched structure on presynaptic neuron
 terminal bouton – slightly enlarged bulb on each end of telodendron (synaptic end bulb, synaptic knob)
 vesicles in the knob contain the neurotransmitter
Term
Process of synaptic transmission
Definition
- when depolarization wave reaches synaptic knob, vesicles fuse with the knob’s cellular membrane and dump neurotransmitter into the synaptic cleft
- neurotransmitters diffuse across the synaptic cleft towards the postsynaptic membrane
- receptors on the postsynaptic membrane bind the neurotransmitter
Term
Types of neurotransmitters
Definition
- excitatory neurotransmitters
 usually cause an influx of sodium so that the postsynaptic membrane moves toward threshold
- inhibitory neurotransmitters
 move the charge w/in the postsynaptic cell farther away from threshold
- Acetylcholine
 can be either excitatory or inhibitory depending on its location in the body
- Catecholamines
 norepinephrine and epinephrine – assoc w/ “fight or flight” rxns of the sympathetic nervous system
 Dopamine – involved w/ autonomic fxns and muscle control
- Gamma-aminobutyric acid (GABA) and glycine-inhibitory
Term
- excitatory neurotransmitters
Definition
 usually cause an influx of sodium so that the postsynaptic membrane moves toward threshold
Term
- inhibitory neurotransmitters
Definition
 move the charge w/in the postsynaptic cell farther away from threshold
Term
- Acetylcholine
Definition
 can be either excitatory or inhibitory depending on its location in the body
Term
- Catecholamines
Definition
 norepinephrine and epinephrine – assoc w/ “fight or flight” rxns of the sympathetic nervous system
 Dopamine – involved w/ autonomic fxns and muscle control
Term
- Gamma-aminobutyric acid (GABA) and glycine-inhibitory
Definition
Term
Recycling the Neurotransmitter
Definition
- Acetylcholinesterase – found on postsynaptic membrane, breaks down acetylcholine
- Monoamine oxidase (MAO) – breaks down norepinephrine
- Catechol-O-methyl transferase (COMT) – breaks down norepinephrine that is not reabsorbed
Term
- Acetylcholinesterase
Definition
found on postsynaptic membrane, breaks down acetylcholine
Term
- Monoamine oxidase (MAO)
Definition
breaks down norepinephrine
Term
- Catechol-O-methyl transferase (COMT)
Definition
breaks down norepinephrine that is not reabsorbed
Term
Central nervous system
Definition
Brain
- cerebrum
- cerebellum
- diencephalon
- brain stem
Spinal Cord
Term
Cerebrum
Definition
- gray matter – cerebral cortex; outer layer of brain, made up of neuron cell bodies
- white matter – myelinated axons in the CNS fibers beneath the cortex and corpus callosum (fibers that connect the two halves of the cerebral cortex
- area of the brain responsible for higher-order behaviors (learning, intelligence, awareness, etc)
- receives and interprets sensory info
- initiates conscious (voluntary) nerve impulses to skeletal muscle
- integrates neuron activity that is normally assoc w/ communication, expression of emotional responses, learning, memory and recall, and other behaviors assoc w/ conscious activity
- gyri (gyrus) – folds in cerebral hemispheres
- fissures – deep grooves separating the gyri
- sulci (sulcus) – shallow grooves separating the gyri – divides the cerebral hemispheres into lobes
- longitudinal fissue – prominent groove that divides the cerebrum into R and L cerebral hemispheres
Term
Cerebral cortex
Definition
outer layer of brain, gray matter, made up of neuron cell bodies
Term
Corpus callosum
Definition
fibers that connect the two halves of the cerebral cortex, myelinated axons in the CNS, white matter
Term
Gyri
Definition
(gyrus) – folds in cerebral hemispheres
Term
Sulci
Definition
(sulcus) – shallow grooves separating the gyri – divides the cerebral hemispheres into lobes
Term
Longitudinal fissure
Definition
prominent groove that divides the cerebrum into R and L cerebral hemispheres
Term
Cerebral hemispheres
Definition
- each hemisphere divided by sulci into lobes
- different lobes specialize in certain fxns
Term
Cerebellum
Definition
- located just caudal to the cerebrum
- area of the brain resp for coordinated movement, balance, posture, and complex reflexes
Term
Diencephalon
Definition
- passageway between brain stem and cerebrum
- structures assoc w/ diencephalon:
- thalamus – acts as a relay station for regulating sensory impulses to the cerebrum
- hypothalamus – interface between the nervous system and the endocrine system
- pituitary – endocrine “master gland” that regulates hormone production and release throughout body
Term
Thalamus
Definition
in diencephalon - acts as a relay station for regulating sensory impulses to the cerebrum
Term
Hypothalamus
Definition
in diencephalon - interface between the nervous system and the endocrine system
Term
Pituitary gland
Definition
in diencephalon - endocrine “master gland” that regulates hormone production and release throughout body
Term
Brain stem
Definition
- connection between the rest of the brain and the spinal cord
- composed of the medulla oblongata, the pons and the midbrain
- resp for basic support fxns of the body
- damage to brain stem can result in resp failure or CV collapse
- many of the cranial nerves originate from the area of brain
Term
Medulla oblongata
Definition
– the part of the brain stem just above (cranial to) the spinal cord
Term
Pons
Definition
a part of the brain stem located just rostral to the medulla oblongata
Term
Midbrain
Definition
mesencephalon, part of the brain stem
Term
Meninges
Definition
- connective tissue layers that surround brain and spinal cord
- contain blood vessels, fluid, and fat
 supply nutrients and oxygen to the superficial tissues of brain and spinal cord
 provide some cushioning and distribution of nutrients for the CNS
- 3 layers
 dura mater – tough, fibrous
 arachnoid – delicate, spiderweb-like
 pia mater – very thin, lies directly on surface of brain and spinal cord
Term
Dura mater
Definition
– the outermost layer of the meninges that covers the brain and spinal cord, toughest of the meninges
Term
Pia mater
Definition
innermost layer of meninges, very thin, lies directly on surface of brain and spinal cord
Term
Arachnoid
Definition
the delicate, weblike layer of the meninges between the dura mater and the pia mater
Term
Myelin sheath
Definition
cell membrane of glial cells (eg oligodendrocytes, Schwann cells) wrapped around an axon; increases speed of impulse conduction along the axon
Term
Oligodendrocytes
Definition
glial cells in the brain and spinal cord whose cellular membrane forms the myelin sheath for axons in the CNS
Term
Schwann cells
Definition
glial cells assoc with the peripheral nerves whose cellular membrane forms the myelin sheath for axons in the PNS
Term
Nodes of Ranvier
Definition
unmyelinated areas of the axon between two adjacent Schwann cells that are involved in rapid conduction of nerve impulses along the axon
Term
Cerebrospinal fluid
Definition
CSF – fluid that bathes and protects the brain and spinal cord from the hard inner surface of the skull and spinal vertebrae
Term
Blood brain barrier
Definition
the functional barrier between the capillaries in the brain and the nervous tissue; anatomically composed of capillary walls w/o the openings found in other capillaries and glial cells
Term
Mnemonics for 12 cranial nerves
Definition
On old Olympus’ towering top, a fine, vocal German viewed some hops
(Olfactory – Hypoglossal)

Six sailors made merry, but my brother said :Bad business, my man.”
(Sensory – Motor)
Term
Ganglion
Definition
cluster of neuron cell bodies outside of the CNS
Term
Somatic reflexes
Definition
a reflex resulting in the stimulation or inhibition of skeletal muscle contraction
Term
Autonomic reflexes
Definition
a reflex that results in inhibition or stimulation of smooth or cardiac muscle or endocrine gland fxn; mechanisms of homeostasis are autonomic reflexes
Term
Withdrawal reflex
Definition
reflex arc in which painful stimulus on skin causes contraction of the affected limb, also called the flexor reflex
- Although the reflex arc may involve several interneurons, several motor neurons and several diff segments of the spinal cord, the reflex occurs w/o the brain being aware of the incident (the limb is withdrawn from the painful stimulus before the brain becomes consciously aware of the painful stimulus
Term
Crossed extensor reflex
Definition
reflex initiated by a stimulation of a limb that results in extension of the limb on the other side of the body
Term
Hyperreflexive
Definition
reflex response that is more pronounced than normal
Term
Hyporeflexive
Definition
– reflex response is less than normal
Term
Stretch reflex
Definition
– reflex initiated by stretch receptors w/in a muscle that results in contraction of the muscle to compensate for the stretching
– simple, monosynaptic or two-neuron reflex arc because it involves only a sensory neuron and a motor neuron (w/ only one synapse between them) w/o any interneurons
– the sensory receptor in a stretch reflex arc is a specialized structure w/in the muscle called a muscle spindle
– if a muscle is stretched, the muscle spindle also stretches and sends impulses via the somatic sensory neuron to the spinal cord
– at the spinal cord, the sensory neuron synapses w/ the motor neuron that innervates the same muscle
– stimulation of the motor neuron causes that muscle to contract in response to stretching of the muscle
– in this way, the body can maintain the tension or tone of a muscle to meet an increased force applied to stretch the muscle, or it can prevent an overstretching of the muscle caused by contraction of opposing muscles
Term
Palpebral reflex
Definition
- Reflex closure of the eyelids when the medial canthus of the eyelids is touched
- Used in anes monitoring to assess the anes depth
Term
Pupillary Light Reflex
Definition
- PLR – reflex in which light is shown in one eye and the pupil constricts in both eyes
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