3 - PHYSIOLOGY OF EXCITATORY TISSUES. IRRITABILITY AND EXCITABILITY. GENERAL AND SPECIFIC PROPERTIES OF EXCITABLE CELLS. MEMBRANE POTENTIAL AND ITS IONIC BASIS.

section

excitable tissues

nervous tissue

RMP (resting membrane potential) depends on

characteristics of resting nerve cell membrane

characteristics of muscle

function of muscle

types of muscle

Endocrine tissue

excitable tissues

tissues capable of generating and transmitting electrochemical impulses along the membrane.

1. Nervous - via neurons

2. muscle - nerves conducting mpulses to muscles → conductors

3. Some endocrine tissues- insulin-releasing pancreatic β cells.

nervous tissue

The human nervous system consists of many nerve cells (or neurons) plus supporting (neuroglial) cells.

• Neurons- communicate

• Respond to stimuli

• Extending out from the cell body are processes called dendrites and axons.

• conduct impulses (with dendrites conducting impulses toward the cell body

• axons conducting impulses away from the cell body

• Neurons can respond to stimuli and conduct impulses because a membrane potential is established across the cell membrane.

• Membranes have a RESTING MEMBRANE POTENTIAL. - an unequal distribution of ions (atoms with a positive or negative charge) on the two sides of the nerve cell membrane.

• This POTENTIAL about -70 mV (with the INSIDE of the membrane negative due to more ions outside nerve membrane)

RMP (resting membrane potential) depends on

• Distribution of ions across membrane (extracellular ions and intracellular ions);

• membrane permeability

• SODIUM - POTASSIUM PUMP actively pumps out 3 Na+ out for every 2K+ in → less positive inside

• membrane is more permeable to k+ so they diffuse back out of cell. less name positive

• These gates represent the only way that these ions can diffuse through a nerve cell membrane.

characteristics of resting nerve cell membrane

• all the sodium gates are closed and some of the potassium gates are open.

• This potential will be maintained until the membrane is disturbed or stimulated.

• If there is a strong stimulus greater than the threshold, an AP will occur. → depolarisation = disturbance

• (*The membrane potential of excitable tissues is more negative (-70 to -90 mV) compared to that of non-excitable tissues.)

characteristics of muscle

1. excitability - responds to stimuli (e.g., nervous impulses)

2. contractility - able to shorten in length

3. extensibility - stretches when pulled

4. elasticity - return to original shape & length after contraction or extension

function of muscle

1. Motion - movement of trunk and limbs

2. maintenance of posture

3. heat production - shivering → vibration causes friction = heat

types of muscle

• skeletal: voluntary muscle. Moves skeleton and striated muscles = heat

• Smooth: involuntary muscle, muscle of the viscera (e.g., in walls of blood vessels, intestine ) - urinary bladder, spindle-shaped, controlled by autonomic system

• Cardiac: involuntary, striated, controlled by autonomic system (controls involuntary muscles)

Endocrine tissue

• The endocrine system includes cells of the glands of the body and the hormones produced by them

• glands are controlled directly by the nervous system as well as by chemical receptors in the blood.

• The endocrine system regulates its hormones through negative feedback, except in very specific cases like childbirth.