The Nervous system (OB2)

function of a nerve cell

basic structural and functional units of the nervous system- neurons.

diagram of a neuron

cell body

contains nucleus, surrounded by cytoplasm with usual organelles

dendrites

short extension of cytoplasm, carry nerve impulses to the cell body.

axon

single extension of cytoplasm, long but may vary in size, carries nerve impulses away from the cell body

Myelin sheath

layer of fatty material, surrounding most axons

Schwan cells

cells which may form myelin sheath

Neurilemma

outer layer of Schwan cell, helps repair injured fibres

Nodes of Ranvier

increase speed of nerve transmission

Axon terminals-

pass the nerve impulse to the next neuron, across a synapse.

functional classifications of neurons

Sensory neuron- carry messages from receptors in sense organs, or skin to CNS

Motor neurons- carry messages from CNS to the muscles and glands, the effectors.

 Interneurons- link between sensory and motor neurons.

structural classifications of neurons

Multipolar neurons- one axon and multiple dendrites extending from cell body, most common, includes motor neurons and most interneurons and CNS. 

Bipolar neurons- one axon and one dendrite, both have branches from the end

Occur in the eye, ear and nose, take impulses from receptors to other neurons.

Pseudo unipolar neurons- one extension only, an axon with a cell body to the side of the axon, most sensory neurons.

diagram of the different types of neurons

synapses

space between two neurons, nerve impulse is carried across it

distinguish between CNS and PNS

the CNS- made up of brain and spinal cord, incoming messages processed outgoing messages inititated

PNS- consists of nerve fibres carrying to and from CNS, 31 pairs of spinal nerves, 12 pairs of cranial nerves

The PNS- carrys nerve impulses to CNS where processed, carries outgoing messages from CNS

PNS VS CNS diagram

cranial and spinal nerves

Cranial nerves- twelve pairs which arise from the brain. Contain fibres that carry impulses into and away from brain.

Spinal nerves- 31 pairs which arise from the spinal cord. They are all mixed nerves containing both sensory and motor fibres. Each nerve is joined to the spinal cord by two roots. The ventral root and the dorsal root.

structure of the spinal cord

actions of the sympathetic and parasympathetic divisions of the autonomic nervous system * table with stuctures

pathway the nerve impulse takes along a neuron

nerve impulse starts at the dendrites, travels to the cell body, down the axon to the axon terminal and then it goes across a synapse to the next neuron.

structure of the spinal cord

Spinal cord extends from the brain to the lower back, it is structured into different regions that coordinate sensory, motor and reflex functions

 The nerve fibres are arranged into nerves, which arise from the brain and spinal cord.

ascending tracts

sensory axons that carry impulses upward, toward the brain.

descending tracts

contain motor axons that conduct impulses downward, away from the brain.

The afferent pathway of the PNS

contains sensory neurons which carry receptors away to CNS, main components- somatic sensory and visceral

somatic- neurons found in skeletal muscles and skin

visceral- neurons found in internal organs.

The efferent pathway of the PNS

motor neurons carry messages away from the CNS to effectors

divided into the somatic nervous system and the autonomic nervous system

somatic nervous system- takes impulse to skeletal musceles

autonomic nervous system- takes impulse to involuntary musceles + glands.

divided into

• sympathetic- acts under stress, enables fight or flight response

• parasympathetic- acts under rest, rest and digest responses

functions of the myelin sheath

1. acts as an insulator

2. protects axon from damage

3. speeds up movement of nerve impulses across axon