The Anatomy and Physiology of

The Nervous SystemDr Ashwini Kalantri

Part II

Nervous System

Peripheral Nervous System

Motor Neurons

Somatic N.S.

Autonomic N.S.

Sympathetic

Parasympathetic

Sensory Neurons

Central Nervous System

Brain Spinal Cord

Sympathetic Nervous System

Organ Effect

Eye Dilates pupil

Heart Increases rate and force of contraction

Lungs Dilates bronchioles

Blood Vessels Constricts

Sweat Glands Activates sweat secretion

Digestive tract Inhibits peristalsis

Penis Promotes ejaculation

Fight or flight

Parasympathetic Nervous System

Works opposite to the sympathetic nervous system

Tries to keep the body at rest.

Functions of the Nervous System

Sensory Function

Sensory receptors gather information

Information is carried to the CNS

Functions of the Nervous System

Motor Function

Decisions are acted upon

Impulses are carried to effectors

Functions of the Nervous System

Integrative Function

Sensory information used to create:SensationsMemoryThoughtsDecisions

Neural Cells

Cell types in neural tissue:

NeuronsNeuroglial cells

(also known as neuroglia, glia, and glial)

Neurons

Myelination of Axons

White Matter

Contains myelinated axons

Considered fiber tracts

Gray Matter

Contains unmyelinated structures

Cell bodies, dendrites

Multipolar UnipolarBipolar

How does the nerve transmit a

signal?

Cell Membrane Potential

A cell membrane is usually electrically charged, or polarized, so that the inside of the membrane is negatively charged with respect to the outside of the membrane.

This is as a result of unequal distribution of ions on the inside and the outside of the membrane.

Distribution of Ions

Potassium (K+) ions are the major intracellular positive ions (cations).

Sodium (Na+) ions are the major extracellular positive ions (cations).

This distribution is largely created by the Sodium/Potassium Pump (Na+/K+ pump).

This pump actively transports sodium ions out of the cell and potassium ions into the cell.

Also due to the presence of ion-selective channels

Resting Potential

Resting Membrane Potential (RMP):

It is a polarized membrane

Inside of cell is negative relative to the outside of the cell, due to distribution of ions inside vs. outside

Na+/K+ pump restores 70 mV difference from inside to outside of cell

RMP = -70 mV

Local Potential Changes

Caused by various stimuli: Temperature changes Light Pressure

Environmental changes affect the membrane potential by opening a gated ion channel

Channels are 1) chemically gated, 2) voltage gated, or 3) mechanically gated

Local Potential Changes

If membrane potential becomes more negative, it has hyperpolarized

If membrane potential becomes less negative, it has depolarized

Graded (or proportional) to intensity of stimulation, meaning the greater the stimulation, the greater the depolarization

If the depolarization is great enough, reach threshold potential

Reaching threshold potential results in a nerve impulse, starting an action potential

Action Potentials

Milliseconds

10

0

+20

+40

2 3 4 5 6 7 8

Mem

bra

ne

po

ten

tial

(m

illi

vo

lts)

Action potential

Hyperpolarization

–40

–20

–60

–80

Restingpotential

Resting potentialreestablished

Pathways

Dr Ashwini Kalantri

+91 9860598097

cell phone

ak@ashwini.co.inemail