The Nervous System
EFE Veterinary Science
Anatomy and Physiology
Image: ship.edu
The Neuron: basic functional unit of the system
Cell body
Axon
Dendrite
Image: urbanchildinstitute.org
Synapse: Where the action is!
Neurotransmiters carry messages along a chain of neurons
ACTH, glutamate, GABA, norepinephrine, serotonin, others
Myelin sheath provides insulation for greater speed
Axons covered with myelin sheaths appear white, forming the
“white matter” of the brain and spinal cord. Cell bodies and
dentrites appear grey, forming “grey matter”.
Image: epsych.msstate.edu
Image: somemedicalthoughts.blogspot.com
Basic Reflex Arc: Patellar tendon reflex
Stretch on patellar tendon->Afferent neuron->
spinal cord->efferent neuron->quadriceps muscle resulting in
extension
Central v Peripheral nervous system
Image: NIM.NIH.org
Image: Daviddarling.info
Spinal Cord
White matter is myelinated
Grey matter contains nuclei
Spinal nerves exit to periphery
The hindbrain
Medulla--nuclei of cranial nerves
Pons—nuclei of cranial nerves
Cerebellum—center of balance and coordination
Kittens with cerebellar hypoplasia
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Midbrain
Also contains the nuclei of the cranial nerves
(more about them later!)
Forebrain
Made up of the diencephalon and the cerebral
hemispheres
Diencephalon
Epithalamus = Pineal gland (remember endocrinology?)
Thalamus: The relay and integration center of the brain
Hypothalamus: Memory and endocrine regulation
Telencephalon = cerebrum = cerebral cortex
This is the grey wrinkly brain that we typically think of.
Animal brains also have an olfactory lobe!
Cortical lobes of the canine brain
Note the large olfactory lobe, which rests just
caudal to the nasal conchae
Animals have a relatively smaller cerebral cortex
….as they do less abstract thinking and reasoning than
humans.
Their more “primitive” brain areas are better developed.
The cerebral cortex
(cerebrum)
Voluntary and conscious
processing:
• Voluntary movement is
initiated
• Sensory input processed
• Thought
• Learning
• Memory
• Judegement
• Language
• personality
Special Pathways in the
cerebral cortex
Several specialized
pathways exist within the
cerebral cortex:
• Visual Pathway
• Vestibular Pathway
• Auditory Pathway
• Somatic motor
pathways
•
•
Pyramidal
Extrapyramidal
• Visceral nervous system
Visual (and pupillary)
pathway
Retina
Optic nerve
Optic chiasm (crossover)
Optic tract (over lateral
thalamus)
• Some to visual cortex
• Some to neuronal
chains for direction of
gaze, accomodation,
pupil size
Vestibular Pathway
Vestibular fibers from the
middle ear
Into brainstem
Some to vestibular nuclei
Some to cerebellum
Some to spinal cord
Some to nuclei for eye
muscles
Conscious perception
centered in the temporal
lobe
Auditory Pathway
Cochlear nerve fibers
Cochlear nuclei in
brainstem
On to 3 sites:
• 2 for reflexes (such as
startle)
• 1 to auditory cortex for
conscious perception of
sound
Somatic Motor Pathways
Controls voluntary
movement of the body
• Lower motor neurons
•
•
connect directly to
muscle fibers
control simple reflex
arcs
• Upper motor neurons
•
•
More complicated
reflexes
Initiate voluntary
movements
2 types of somatic
motor pathways
Pyramidal
• fine motor control
Extrapyramidal
• Coarser movements
(gross motor)
Meanwhile, the
autonomic nervous
system
Essentiallly allows us to
run on “autopilot” with our
basic functions
Involuntary and generally
outside of our awareness
Can be influenced by
environment, emotion and
drugs and medications
The Autonomic
Nervous System
• Involuntary system
• Controls internal
environment of the
animal
• Senses changes and
sends signals to:
•
•
•
Endocrine glands
Smooth muscle in
organs
Cardiac muscle
The Autonomic
Nervous System
Two major branches:
• Sympathetic
• Prepares for fight or
flight response
• Increase heart rate
• Dilate pupils
• Bronchodilation
• Parasympathetic
• Opposite to
sympathetic
• Mainly vagus nerve
• Slows heart rate
• Constricts pupils
The Visceral Nervous
System
Provides central (brain)
control over maintenance
of internal environment
• Hypothalamus
• Pituitary gland
• Visceral afferents
• Visceral efferents
• Limbic system
Side note on the
Limbic System
Most influenced by
olfactory input
Also receives optic,
auditory and touch from in
and outside the body
Involved in emotional
behavior: rage, fear, etc.
Also processing memories
and “filing” them for later
retrieval
Other structures
associated with the
nervous system
Meninges
Cerebrospinal fluid
Cranial nerves (12)
Spinal nerves
Peripheral nerves
Meninges
Tough fibrous membranes
surrounding the brain and
spinal cord
3 layers:
Dura matter
Subarachnoid
Pia matter
Meningitis
Epidural
Cerebrospinal fluid
Clear fluid
Surrounds the brain and
spinal cord
Within the arachnoid space
Produced within the
ventricles of the brain
The 12 Cranial
Nerves
Responsible for sensory
and motor function of head
and face
Also major sensory
functions
Each originates in a
specific place in the brain
Don’t worry, you will get
to memorize them later!
(Lawhead page 150)
Spinal Nerves
Dorsal spinal nerve roots
carry sensory information
Ventral roots carry motor
function
In the spinal cord, the grey
matter lies inside the white
matter; in the brain, it is
opposite.
Peripheral Nerves
Carry nerve impulses
throughout the body
Brain -> spinal cord ->
spinal nerve -> peripheral
nerve for motor function
Peripheral nerve -> spinal
nerve -> spinal cord ->
brain for sensory
Usually combination of
both.
So, don’t be nervous! You’ll get this!
(THE END)