5.3.2(Structure and function of neurones)

Describe the structure of neurons

• The plasma membrane has many gated ion channels that control the entry or exit or sodium, potassium or calcium ions

• They generally consist of a cell body, an axon and dendrites

Describe the role of axon, cell body and dendrites

• Axon - carried impulses away rom the cell body

• Cell body - contains the nucleus, many mitochondria and ribosomes

• Dendrites - connect to other neurons and carry impulses towards the cell body

Name the 3 types of neurones

• Motor neurone

• Sensory neurone

• Relay neurone

Describe the role of each type of neurone

• motor neurone - Carry action potentials from the CNA to an effector

• Sensory neurone - Carry action potentials from a receptor to the CNS

• Relay neurone - Connect sensory and motor neurones

Describe the structure of a motor neurone

• They have their cell body in the CNS and have a long axon that carries the action potential out to the effector

• They have many short dendrites to carry nerve impulses from the CNS to the cell body

Describe the structure of a sensory neurone

• Have one long dendron and short dendrites carrying the action potential from a receptor to the cell body which is positioned just outside the CNS

• They have a short axon carrying action potential from cell body to CNS

Describe the structure of the relay neurone

• They have many short dendrites and a short axon.

Describe the similarities and difference between the sensory and motor neurones

• Diff - In sensory neurones the cell body is outside of the CNS while in motor it is inside the CNS

• Diff - Sensory neurones have a short axon while motor neurones have a long axon

• Diff - Sensory neurones have a long dendron while motor neurones have short dendrites

• Diff - Sensory neurones carry action potentials to CNS while motor neurones carry action potentials away from the CNS

• Sim - Both are myelinated

Describe what is meant by a myelinated neuroone

• It is a neurone which is insulated by a myelin sheath

Describe the structure of the myelin sheath

• It is a fatty sheath which formed from Schwann cells

• The sheath is wrapped in many layers around the cell

• at 1-3 mm intervals there are gaps in the myelin sheath - nodes of Ranvier

Describe the role of the myelin sheath

• It insulates the axon and prevents the diffusion of ions

• This makes the conduction more rapid

Describe the role of the nodes of Ranvier

• Ions diffuse only at the nodes, causing the impulse to jump along the axon in the saltatory response

Describe structure of non-myelinated neurones

• These neurones are associated with Schwann cells

• Several neurones may be loosely wrapped by one cell - offering less insulation

• The action potential passes as a wave along the neurone

Describe the advantages of myelin sheaths

• Can transmit action potentials much quicker than non-myelinated

• They can carry action potentials over long distances - faster response to stimuli