1. The Nervous system
MSU AGR 143

2. 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

3. 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

4. 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

5. 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)

6. 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.

7. 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.

8. 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?

9. 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.

10. 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!

11. 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

12. 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.

13. 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

14. Brain Structure and Function
Brain Stem-
Controls respirations, circulation, heart rate, blood pressure
Damage to this region of the brain instantly can cause death

15. Brain Structure and Function
Cerebellum- control the coordination of movement
Monitors signals from the eyes and the balance center to aid in coordination

16. 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

17. 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

18. Diencephalon Thalamus- important relay center
Epithalamus- includes pineal gland (melatonin)
Hypothalamus- autonomic activities, behavior
Ventral- pituitary gland

19. Metencephalon Cerebellum- timing and execution of movements
Pons- bridge from one hemisphere of cerebellum to the other

20. 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

21. 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

22. 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.

23. 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.

24. 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

25. 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

26. Clinical Practice
Nystagmus- eyes jerk back and forth in a rhythmic motion
Ataxia- uncoordinated movement
Atrophy-muscles begin to shrink

27. 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

28. 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