Transcript Nerve Cell Physiology

Nerve Cell Physiology
Obert Tada
Dept of Livestock & Wildlife Management
Content
Introduction
Structure of types of neurones
Membrane excitation & generation of
action potentials.
Introduction
Nervous System
Endocrine System
Complexity
More structurally complex;
can integrate vast amounts
of information and
Less structurally complex
stimulate a wide range
of responses
Structure
System of neurons that
branch throughout the
body
Endocrine glands secrete hormones
into the bloodstream where they are
carried to the target organ
Hormones circulate as chemical
Neurons conduct electrical
messengers throughout the body via
signals directly to and from
Communication
the bloodstream; most body cells are
specific targets; allows fine
exposed to the hormone and only
pinpoint control.
target cells with receptors respond
Response Time
Fast transmission of nerve
impulses up to 100m/sec
May take minutes, hours or days for
hormones to be produced, carried by
blood to target organ, and for
response to occur
The Vertebrate Nervous System
 Nervous tissue senses stimuli and transmits signals from
one part of the animal to another.
 A neuron is a cell specialized to conduct electrochemical
impulses called nerve impulses or action potentials.
 Consists of
 Cell body
 Dendrites, extensions that conduct impulses to the cell body
 Axons, extensions that transmit impulses away from the cell
body
 What does it look like?
Neuron
Neuron cont’d
 All neurons outside the CNS conduct impulses along hairlike cytoplasmic extensions, the nerve fibers or axons.
 The axons connecting spinal cord to the foot can be as
much as 1m long.
 Axons grow out of the cell body, which houses the
nucleus as well as other organelles such as the ER.
 Nerve impulses are generated in short, branched fibers
(dendrites) and also in the cell body.
 The impulses are then conducted along the axon.
Neuron cont’d
 Many axons are covered with a glistening fatty sheath,
the myelin sheath (greatly-expanded plasma membrane
of an accessory cell, the Schwann cell).
 Schwann cells are spaced at regular intervals along the
axon.
 Their plasma membrane is wrapped around and around
the axon forming the myelin sheath.
 Where the sheath of one Schwann cell meets that of the
next, the axon is unprotected.
 This region, the node of Ranvier, plays an important part
in the propagation of the nerve impulse.
Type of Neurons
 There are three major classes of
neurons.
A. Sensory neurons
B. Interneurons
C. Motor neurons
Sensory Neurons
 These run from the various types of stimulus
receptors to the CNS (brain & spinal cord).
 e.g. touch, odour, taste, sound, vision
 The cell bodies of the sensory neurons leading to
the spinal cord are located in clusters, called
ganglia, next to the spinal cord.
 The axons usually terminate at interneurons.
Interneurons
 These are found exclusively within the spinal cord and
brain.
 They are stimulated by signals reaching them from:
 sensory neurons
 other interneurons or
 both.
 Interneurons are also called association neurons.
 It is estimated that the human brain contains 100 billion
(1011) interneurons averaging 1000 synapses on each;
that is, some 1014 connections.
Motor neurons
 These transmit impulses from the CNS to the muscles
and glands that carry out the response.
 Most motor neurons are stimulated by interneurons,
although some are stimulated directly by sensory
neurons.
 Diagram….
Organization of Neurons