Chapter 3 - Neurones

typical neurone transmission pathway - transmits electrical and chemical signals

synapse

junction between the axon terminal of one neurone with dendrite of another adjacent neurone

dendrites VS axon

dendrites carry nerve impulses TOWARDS cell body

axons carry nerve impulses AWAY from cell body

types of neurone - multipolar

• one axon and multiple dendrites extending from cell body

• structure for most motor and interneurones

type of neurone - bipolar

• one axon and one dendrite extending from cell body

• structure occurs in eye, ear and nose

type or neurone - unipolar

• one extension from cell body which is the axon

• structure typically found in invertebrates

type of neurone - pseudounipolar

• one axon extending from cell body

• most sensory neurones are this type

generation of action potential

why nerve cell membrance ONLY relay signals in ONE direction

when action potential is generated, section of membrane behind the action potential is in its refractory period, thus membrane potential not at -70mv(resting potential)

transmission of impulses along MYELINATED axon - saltatory conduction

• cause action potentials to jump from one node of ranvier to another

• local current flow distance is longer

trnamsission of impulses along UNMYELINATED axon - continuous propagation

• depolarization of one area on membrance causes a local current flow between neighbouring areas on the membrane immediately adjacent to the site of the original stimulus

• each action potential generates another action potential just infront of it

• local current flow distance is shorter

role or myelin sheath

insulates the axon to speed up nerve impulse transmission

WHY local current flow distance longer but nerve impulse transmission faster?

allows electrical signals to jump farther along axon before needing to regenerate at another ion channel

synaptic transmission

receptor

• detects stimuli

• similar receptor cells are grouped together in a sense organ

• provides SOMATIC and SPECIAL sensation

• somatic sensation - originate from receptors found in more than 1 location in body, EG: touch, pain

• special sensation - originate from receptors restricted to a particular area of the body. EG: sight, taste

reflexes

• rapid, automatic response to a change in the external or internal environment

• mostly coordinated by spinal cord

4 properties of reflexes

1) stimulus is required, not spontaneous

2) reflex is involuntary, occur without consious thought

3) response is rapid, only small number of neurones involved

4) response is stereotyped, occurs in same way every time

purpose of reflexes

rapid and involuntary to prevent further or long term injury to body