A&p2 L01: Nervous Tissue

Front 1

Explain the organisation of the nervous system.
(2)

Back 1

CENTRAL NERVOUS SYSTEM (brain & spinal cord);
PERIPHERAL NERVOUS SYSTEM (nerves & sensory receptors);

Front 2

Explain the function of the Central Nervous System.
(3 - Princ cc; Integ ii; Det ar)

Back 2

Principal control centre of the body;
Integrates incoming information;
Determines appropriate responses.

Front 3

Explain the function of the Peripheral Nervous System.
(1 - Comm)

Back 3

PNS Nerves are communication lines to & from the CNS

Front 4

Name the different parts of the neuron cell.
(9 - SND ACT SSN)

Back 4

SOMA: body of cell;
NUCLEUS: the organelle in the cell body of the neuron that contains the genetic material of the cell;
DENDRITES: highly branched fibres (dendrite spines) that extend from the cell body. Specialised to receive neural impulses and transmit them to the cell body;
AXON: the long extension of a neuron that carries nerve impulses away from the body of the cell;
COLLATERAL BRANCH: formed off of the axon;
TERMINAL BRANCHES: distal end of axon which divides extensively;
SYNAPTIC TERMINAL: the end of a terminal branch;
SCHWANN CELL: plasma membrane which wraps around the axon many times forming the myelin sheath;
NODES OF RANVIER: gaps that occur between the myelin sheath.

Front 5

Explain the role of the peripheral nervous system in maintaining homeostasis.
(conditions and decisions)

Back 5

The nerves of the PNS continually inform the CNS of changing conditions and then transmit decisions to appropriate muscles and glands that make any adjustments needed to maintain homeostasis.

Front 6

Relate the structure of cells in the CNS to their function.

Back 6

NEURONS transmit signals.

GLIAL CELLS protect and support the neuron.

Front 7

Explain the structure and function of the cell body, dendrites and axon in a neuron.

Back 7

The cell body contains the nucleus and most organelles;
Many dendrites and a single axon extend from the cell body.
Dendrites are branched fibres which extend out from around the cell body. Dendrites receive neural impulses and transmit them to the cell body;
Axons send a nerve impulse to the synaptic terminal at the axons distal end to be passed to either another neuron, a muscle or gland.

Front 8

Define the term neural impulse.

Back 8

A neural impulse, also known as action potentials, are the electrical signals received and transmitted by neurons.

Front 9

Describe the structure and function of a myelin sheath including the Schwann cells and the nodes of Ranvier.

Back 9

The myelin sheath is a plasma membrane made of a white fatty substance. This plasma membrane is wrapped around the axon many times and provides excellent insulation that speeds the conduction of nerve impulses. In a peripheral neuron the myelin sheath is covered by an outer cellular sheath. Both the myelin and cellular sheaths are formed by support cells known as Schwann cells. Gaps known as the nodes of Ranvier occur in the myelin sheath between Schwann cells. At these gaps the axon is not insulated with myelin. This allows for saltatory conduction along the axon.

Front 10

Distinguish between nerve and tract, ganglion and nucleus.

Back 10

A NERVE is a collection of nerve fibres (axons) in the PNS.

A TRACT is a collection of nerve fibres (axons) in the CNS.

GANGLIONS are the cluster of neuron cell bodies within the PNS.

NUCLEI are the cluster of neuron bodies within the CNS.

Front 11

Distinguish between sensory neurons, motor neurons and interneurons.

Back 11

Afferent (SENSORY) neurons in the PNS transmit information to interneurons in the CNS.

INTERNEURONS transmit information to appropriate efferent (motor) neurons.

Efferent (MOTOR) neurons transmit the message to the effectors - the muscles and glands.

Front 12

Distinguish between depolarised and hyperpolarised.

mV = membrane voltage/potential

Back 12

DEPOLARISATION is when the mV of a neuron becomes less negative than the neuron's resting mV. A depolarised neuron is said to be excitatory because it is closer to transmitting a neural impulse.

HYPERPOLARISATION is when the mV of a neuron becomes more negative than the neuron's resting mV. A hyperpolarised neuron is said to inhibitory because its ability to generate a neural impulse has decreased.

Front 13

Distinguish between depolarised and hyperpolarised action potential.

mV = membrane voltage/potential

Back 13

When a DEPOLARISED neuron's action potential becomes more positive than that of the resting neuron it becomes closer to transmitting a neural impulse.

When a HYPERPOLARISED neuron's action potential becomes more negative than that of the resting neuron its ability to generate a neural impulse decreases.

Front 14

Distinguish between gated, ligand gated and non-gated voltage channels.

Back 14

If an electrical event opens a gated channel, it is called a voltage-gated channel.

If a chemical signal opens a gated channel, it is called a ligand-gated channel.

Non-gated channels are always open and are not influenced by extrinsic forces. They are important, though, because they preserve and maintain the resting membrane potential.

Front 15

Explain how the resting potential is generated in a cell.

Back 15

Sodium-potassium pumps in the plasma membrane continuously transport Na+ & K+ in and out of the neuron in order to maintain the resting potential of the neuron.

Front 16

State the function of an action potential.

Back 16

An action potentials function is to transfer a signal across greater distances through the neuron.

Front 17

Identify the movement of ions that generate the two phases of an action potential, depolarisation and repolarisation.

Back 17

DEPOLARISATION occurs when a stimulus causes sodium ions to move in to the neuron. The membrane potential becomes less negative. It is excitatory.

REPOLARISATION occurs as the action potential moves down the axon. Changes in the permeability of the ion channels bring the membrane back to its relatively negative state.

Front 18

Distinguish between the absolute and the relative refractory periods.

Back 18

During the ABSOLUTE REFRACTORY PERIOD cannot transmit another action potential because the voltage-activated Na+ channels are inactivated. When enough Na+ channel gates have been reset the neuron enters a RELATIVE REFRACTORY PERIOD during which the axon can transmit impulses but the threshold is high.

Front 19

Explain the all-or-none phenomenon as it relates to action potentials.

Back 19

The membrane potential either exceeds threshold levels and transmits an action potential or it doesn't - all or nothing. There is no variation in the strength of the impulse.

Front 20

Compare how an action potential is propagated in an unmyelinated and a myelinated neuron.

Back 20

CONTINUOUS CONDUCTION: Across UNMYELINATED neurons the transmission of a neural impulse is smooth and progressive.

SALTATORY CONDUCTION: Across myelinated neurons the voltage-activated ion channels are concentrated at the gaps between Schwann cells (myelinated areas) known as the nodes of Ranvier. The action potential jumps along the axon from one node to the next as the next node is depolarised.