Download The Nervous system - Locust Trace Veterinary Assistant Program

THE NERVOUS
SYSTEM
MSU AGR 143
Functions of the Nervous
System
■ Initiate/regulate movement of body parts
■ Regulate secretions from glands
■ Gather info from environment- pain, temp, pressure, CO2, O2
■ Maintain an approximate consciousness
■ Stimulate thirst, hunger, fear, range and sexual behaviors
How the System is Divided
■ CNS- Central Nervous System- made up of the brain and
spinal cord
■ PNS- Peripheral Nervous System- made up of all the other
nerves
Neuron Function
■ Neuron- Specialized cell that lies
within the nervous system
– Conducts electrochemical
signals
■ Two regions– Larger region-body
– Long, thin region-axon
■ Axon-transmits signals long
distances to other structures
– Group of axons= nerves
■ Dendrites- shorter extensions,
receive signals from other
neurons
Schwann Cells
■ Schwann Cells- have extensions of the
cytoplasm and cell membrane that wrap
around the axons of neurons.
– Schwann cells increase the
diameter
– Create myelin sheath
– Increases the speed of the nerve
signal
– Not all nerves have a myelin
sheath.
■ Myelinated nerves- transport a signal
much faster than nonmyelinated
nerves. (nerves within a myelin sheath=
myelinated)
3 Classifications of Neurons
■ Sensory Neurons- deliver a signal from a specialized receptor
to the CNS
– Receptors detect light, sounds, etc.
■ Interneurons- responsible for delivering a signal from one
neuron to another.
– Provide complex pathways present in the brain and
spinal cord.
■ Motor Neurons-deliver the signal from the CNS to the muscle
or gland stimulated for a response.
Neuron Function
■ Nerve impulse= electrochemical signal that transmits along
the length of the neuron.
– Complex process
– Requires input of energy by the cell
■ Resting neuron- interior of the cell is more negatively charged
than the extracellular region.
■ Polarization- used to describe the condition in which one
region of a cell has a different charge than the adjacent
regions.
Neuron Function
■ Reflex arc- simplest unit of function within the
nervous system.
■ Reflex= body acts without requiring conscious
thought.
■ Ex. Cat walking on a hot stove, quickly pulls
back to prevent further injury.
■ How does it work?
How does it work?
■ Reflex arc begins with a stimulus= hot stove
■ Sensors in the foot detects heat, triggers nerve impulse in the
sensory nerve.
■ Sensory nerve synapses onto the interneuron within the
spinal cord.
■ Interneuron stimulates other interneurons or goes directly to
the motor neurons.
■ Motor Neuron stimulates the muscle to pull back the leg,
preventing further injury.
How does it work?
■ No signal is sent to the brain
■ Entire reflex occurs at the level of the spinal cord
■ During reflex actions the brain does receive signals of events.
■ Cat required no input form the brain to pull it’s foot away
■ But… the brain was sent signals telling the animal that the
stove was hot
■ As a result the cat changed its course and the reflex
prevented a severe burn!
Brain Structure and Function
■ Nervous system divides into central nervous system (CNS)
and the Peripheral nervous system (PNS)
– PNS-detects stimuli and informs the CNS
– PNS- carries the signal to cause a response at the level
of the muscle/gland
■ CNS- receives all the signals from the PNS and coordinates all
activity.
– Spinal cord and brain make up the CNS, skull and
vertebrae protect CNS
Brain Structure and Function
■ Meninges- a group of three membranes wrap around the
brain and spinal cord
■ CNS is bathed in cerebrospinal fluid, adds protection.
■ CSF gives cushioning when trauma occurs to the head or
backbone.
Brain Structure and Function
■ Brain is divided into 3 regions:
■ Cerebrum- controls voluntary movement and thoughts.
■ Cerebellum- coordination in the animals movement.
■ Brain stem- controls most of the functions necessary to
maintain life
Brain Structure and Function
■ Brain Stem– Controls respirations, circulation, heart rate, blood
pressure
– Damage to this region of the brain instantly can cause
death
Brain Structure and Function
■ Cerebellum- control the coordination of movement
■ Monitors signals from the eyes and the balance center to aid
in coordination
■
Brain
Structure
and
Function
Cerebrum- largest and most cranial structure of the brain
– Divided into two halves or hemispheres
– Hemispheres are joined by white matter
■ White matter is made out of myelinated axons
■ Grey matter- the outer region, or cerebral cortex, consists
of cell bodies, which have elevations and grooves that
increase the surface area within the brain.
– Controls thought, learning, judgment, language, and
personality
Parts of the Cerebrum
■ Diencephalon- thalamus, epithalamus, hypothalamus and
third ventricle
■ Mesencephalon (midbrain)- cerebral peduncles and four
colliculi – nerve fibers that connect the spinal cord and
brinstem to the cerebral hemispheres
■ Metencephalon- cerebellum (dorsal) and pons (ventral)
■ Myelencephalon- medulla oblongata – autonomic centers
Diencephalon
■ Thalamus- important relay center
■ Epithalamus- includes pineal gland (melatonin)
■ Hypothalamus- autonomic activities, behavior
– Ventral- pituitary gland
Metencephalon
■ Cerebellum- timing and execution of movements
■ Pons- bridge from one hemisphere of cerebellum to the other
Anatomy and Function of the Spinal
Cord
■ Spinal cord is the second
component of the CNS and links the
CNS and the PNS
■ Extends from base of the brain thru
canal formed by vertebrae
■ White matter-outer region,
myelinated nerves
■ Grey matter- inner portion, cell
bodies
Sensory Somatic and
Autonomic Nervous Systems
■ PNS is divided into the sensory somatic system and the
autonomic system
■ Sensory somatic system= all motor activity and detects
change in the environment
Autonomic system= involuntary system that controls the internal
environment of the animal
Sensory Somatic System
■ Includes 12 pairs of cranial nerves
– Cranial nerves enter the brain directly, not the spinal
cord
■ Spinal nerves, 36 pairs- nerves enter spinal cord at each
vertebral opening, dorsal and ventral branches.
– Dorsal and ventral branches join to create a mixed
nerve.
Autonomic System
■ Two divisions: sympathetic and parasympathetic systems
■ Sympathetic= fight or flight
■ Sympathetic stimulation- HR and BP increases
– Blood shift away from the skin and abdominal organs to
muscles, brain and heart.
– Bronchi open to allow more air into the lungs
– Pupils dilate- all in prep for physical activity such as
running from a preditor.
Autonomic System
■ Parasympathetic system- opposite effect of the sympathetic
system
– Activation of the parasympathetic system slows HR and
lowers BP
– Pupils constrict
– Blood shifts back to the skin and abdominal organs
Enteric Nervous System
■ Network of motor and sensory neurons in the GI tract and
glands
■ Influenced by parasympathetic and sympathetic systems
– **Functional without input from outside viscera
Controls local events in GI tract
Clinical Practice
■ Nystagmus- eyes jerk back and forth in a rhythmic motion
■ Ataxia- uncoordinated movement
■ Atrophy-muscles begin to shrink
Anatomy and Function of the
Spinal Cord
■ Myelogram- diagnostic test, dye is injected into the epidural
space (CSF), radiograph is taken to trace the dye. Dye is
visible on the radiograph and helps show location of a
problem
Summary
■ CNS= brain and spinal column
■ PNS= nerves in the limbs
■ PNS divided into sensory somatic and autonomic system
■ The Nervous System in its entirety controls many body
functions