Nervous System

Page 1

Nervous System Lecture – Organization and Histology OUTLINE

Intro to the nervous system (Fig 12.1)

NS is apart of the homeostatic pathway

Central nervous system

responsible for :

Integration processing

coordination

memory

learning

emotions

Peripheral nervous system

Subdivided into sensory and motor

sensory info into the CNS

motor commands to the effectors

Afferent nervous system

sensory comes FROM CNS

receptors to CNS

Efferent nervous system

cns TO EFFECTORS

motor

Somatic nervous system

skeletal muscles

voluntary control

Autonomic nervous system

smooth muscle, cardiac muscle , adipose tissue , glands

involuntary control

Parasympathetic

calm state of the body

REST and DIGEST

Sympathetic

prepared for action

FIGHT or FLIGHT

Cells that make up the nervous system (Fig 12.6, 12.5)

Neuroglia or glial cells- they reside all in neural tissue

support

nourish

protect neurons

out number neurons 10 to 1

Six types

CNS: astrocytes, oligodendrocytes, microglia, ependymal cells

Astrocytes

largest + most numerous

shield neurons

maintain blood brain barrier

some neural tissue repair

embryonic neural development

controls interstitial enviorment

- nutrient , ions , neurotransmitter uptake

*phospholipid bilayer

hydroPHILLAC heads

hydroPHOBIC tails

Oligodendrocytes

cause myelination (wrapping around multiple cells )

only work in the CNS

myelination

- important to how the cell functions

Microglia

the tiniest glial cells

phagocytes (they engulf and destroy ellular debris and waste products )

Ependymal cells

found in the ventricles of the brain and the central canal of the spinal cord

make cerebral spinal fluid

PNS: Schwann cells, satellite cells

Satellite cells

surround neurons in ganglia

regulate nutrient and waste exchange

ganglia

location of cell bodies of neurons

Schwann cells

performs myelination of the PNS neurons

can do some regeneration of axons

only wraps around ONE neuron

Neurons (Fig 12.2)

Neurons respond to an action potential, a sudden change in electrochemical force that propagates on the membrane surface of a neuron

Parts of the neuron

Cell body or soma

synthesize proteins

a nucleus

cytoplasm is called PERIKERYON , has NO centrioles so it does NOT divide (mitosis)

can also receive signals

Nissl bodies

rough endoplasmic reticulum

Dendrites

short slender

receive signals to transmit to the cell body

Axon

single projection off cell body

propagates action potentials

Axon Hillock

generates the first action potential

is between cell body and the axon

Initial segment

the start of thhe axon

Axoplasm

cytoplasm of axon

Axolemma

cell membrane of the axon

Axon collaterals

allow for the message (signal) to travel to multiple effectors

Synaptic terminal (Fig 12.30

contain neurotransmiter

send signal to next cell

Axons are surrounded by a myelin sheath (Fig 12.7)

multilayered lipid protein covering of an axon

In the PNS Schwann cells

Nodes of Ranvier

In the CNS, oligodendrocytes

Unmyelinated – not completely myelinated (Fig 12.7)

Axoplasmic transport - transport of materials NOTHING TO DO WITH ACTION POTENTIAL

Anterograde - cell body to the axon terminals

protein used is KINESIN

Retrograde- AXON TERMINALS TO ELL BODY

protein used DYNEIN

Types of neurons

Structural classification (Fig 12.4)

Multipolar neurons

most common

goes to skeletal muscles

Bipolar neurons

special senses eyes ears toungue etc)

Unipolar neurons

PNS -sensory organs

Anaxonic neurons

found in the brain

cannot generate action potentials because it has no axon

associated with memory and learning

Functional classification

Sensory (afferent) neurons – transmit nerve impulses from receptors in the skin, sense organs, muscles, joints and viscera toward the CNS

somatic sensory neurons (monitors external environment) - skeletal muscles skin joints

visceral sensory neurons (monitors internal environment)- glands organs blood vessels

Motor (efferent) neurons – transmit nerve impulses from the CNS to effectors

somatic motor neurons – innervate skeletal muscles

visceral motor neurons – innervate smooth muscle, cardiac muscle, glands and adipose tissue

Interneurons (association neurons) – distribute sensory information and coordinate motor activity; information processing; memory, planning and learning; brain and spinal cord

Damage and Repair

PNS – dendrites and myelinated axons can be repaired if cell body is intact and Schwann cells are active

CNS – little or no repair even if the cell body is intact

Review questions from your book:

What is a receptor? What is an effector?

Distinguish between the central and peripheral nervous systems and between visceral and somatic divisions of the sensory and motor systems.

What is another name for the visceral motor nervous system? What are its two subdivisions? What are their functions?

Sketch a multipolar neuron and label its soma, dendrites, axon, synaptic knobs (bulbs), myelin sheath, and the nodes of Ranvier.

Explain the difference between a sensory neuron, a motor neuron, and an interneuron.

What is the functional difference between a dendrite and an axon?

How do proteins and other chemicals synthesized in the soma get to the synaptic knobs? By what process can a virus that invades a peripheral nerve fiber get to the soma of that neuron?

How is a glial cell different from a neuron? List the six types of glial cells and discuss their functions.

How is myelin produced? How does myelin production in the CNS differ from that in the PNS?

How can a severed peripheral nerve fiber find its way back to the cells it originally innervated?