The Nervous SystemThe Nervous SystemChapter 6Chapter 6

The Nervous SystemThe Nervous SystemChapter 6Chapter 6

The Nervous system has three major functions:

Sensory

monitors internal & external environment through presence of receptors

Integration

Interprets sensory information

Motor

response to information processed through stimulation of effectors

Two Anatomical Divisions Central nervous system (CNS)

Brain Spinal cord

Peripheral nervous system (PNS) All the neural tissue outside CNS Afferent division (sensory input) Efferent division (motor output)

Organization of the Nervous System

Afferent vs Efferent

Afferent Nerves

Sensory Nerves Receive Information Transmit sensory

information gathered from the skin, muscles, and joints to the CNS

Efferent Nerves

Motor Nerves Send information on Carries information from

the CNS out to the muscles and glands

Sensory nerve cells: Afferent pathwayCNS (brain and spinal cord): Integration centersMotor nerve cells: Efferent pathway

Organization of the Nervous System

Brain & spinal cord

Cells of the Nervous System

Two types of neural cells in the nervous system:

Neurons

Process, transfer, and store information

Neuroglia – (also called “glial cells”)

Support and protect neurons

Structure of a Neuron

•Most axons of the nervous system are surrounded by myelin

•The presence of myelin speeds up the transmission of signals along the axon

•Myelin will get laid down in segments along the axon, leaving unmyelinated gaps known as “nodes of Ranvier”

ELECTRICITY!!!

Conductivity: the property of neurons that give them the ability to transmit nerve impulses

Electrical impulses (action potentials) are “all-or-none” responses

Axon terminals do not actually touch the other neuron or muscle. The gap

is called the synapse.

Neurotransmitters are chemical messengers.

The Structure of a Typical Synapse

Classification of Neurons

Structural classification based on number of processes coming off of the cell body

We will talk about three neuron structures:

1.Multipolar

2.Bipolar

3.Unipolar

Multipolar neuron

• multiple dendrites

• single axon

• most common type

• ALL motor neurons are multipolar

Bipolar neuron• two processes coming off cell body

• one dendrite • one axon

• only found in eyes, ears & nose• Process sensory information

Unipolar neuron

• single process coming off cell body

• dendrites at one end

• axon makes up the rest of the process

• some sensory neurons in PNS are unipolar

Anatomical structure of Nerves

Fig. 14.6

Efferent Divisions

Somatic Nervous System Voluntary Stimulates skeletal

muscles Stimulates them to

contract

Autonomic Nervous System Involuntary Controls cardiac muscle of

the heart and smooth muscle of internal organs

2 Categories Sympathetic

Fight or Flight response Releases adrenaline

Parasympathetic Rest and digest response Day-in-day-out functions

Reflexes (Simple, rapid, involuntary, programmed responses to stimuli)

Somatic Reflexes Stimulation of skeletal

muscles Ex: Withdrawing hand

from something hot before you even realize it is hot

Fast because doesn’t travel to brain and back (sensory neuron spinal cord motor neuron)

Autonomic Reflexes Send involuntary stimuli

to cardiac muscle of heart and smooth muscle of internal organs

Ex: Digestion, elimination, sweating, blood pressure

Nervous System Overview

Nerve Impulses

Synapses In Detail