Animal physiology Flashcards
The nervous system
The mammalian nervous system is composed of the brain and spinal cord (CNS), as well as the cranial and spinal nerves (PNS). Information is transferred as nerve impulses which transfer along nerve cells at high speed.
Sensory neurone
Transmits impulses from receptor cells to CNS
Intermediate neurone
Transmits impulses from sensory neurone to motor neurone
Motor neurone
Transmits impulses from the CNS to effector cells ie a muscle or gland
Structure of motor neurone
A motor neurone has many branched dendrites to provide a large surface area for the ending of other neurones. The axon is very long so the impulse can be conducted over a long distance. The ends of the axon have a large number of mitochondria together with vesicles containing transmitter substances. The vesicles pass the impulse to the effector cell. The mitochondria are used in aerobic respiration to provide energy for active transport
How does Myelin sheath cells increase the speed of transmission
Myelin speeds up the rate at which action potentials travel, by insulating the axon membrane. Sodium and potassium ions cannot flow through the myelin sheath, so it is not possible for depolarisation or action potentials to occur in parts of the axon which are surrounded by the myelin sheath. Action potentials can only occur at the nodes of Ranvier, where all the channel proteins and pump proteins are concentrated. Thus action potentials jump’ from one node to the next, This is called saltatory conduction.
A reflex arc
The pathway along which impulses are transmitted from a receptor to an effector without involving conscious regions of the brain
Reflex action
A fast automatic response to a stimuli, the response to each specific stimulus is the same
Hormonal communication
Hormones are made in endocrine glands, which are ductless, They are released into the blood and bind to receptors on target cells
What are nerve impulses
They travel along the cell surface membrane of a neurone, they are brief changes in electrical charge distribution across the cell surface membrane called action potentials.
Resting potential
The potential difference, is often between −60mV and −70mV. In other words, the electrical potential of the inside of the axon is between 60 and 70mV lower than the outside. This difference is the resting potential
Maintaining resting potential
The resting potential is produced and maintained
by the sodium–potassium pumps in the cell surface
membrane. Three sodium ions are removed from the axon for every two potassium ions brought in, using the energy from ATP. There are fewer sodium channels then pottasium channels. Therefore, some potassium diffuses back out again faster than sodium diffuses back in. There are many large, negatively charged molecules inside the cell that attract the potassium ions reducing the chance that they will diffuse out. So more negative in membrane
Generating an action potentil
When there is a change in the potential difference across the CSM, some voltage gated sodium channels open. Na+ starts to diffuse in down the electrochemical gradient. The potential difference across the membrane becomes less negative this is depolarisation, which causes more Na+ to diffuse in. The potential difference reaches the threshold potential which causes many channels to open so Na+ floods in, making pd more positive. After a delay the voltage gated sodium channels close and sodium stops diffusing in. Voltage gated potassium channels open and potassium diffuses out down the concentration gradient. Pd across CSM becomes negative again (repolarisation). Pd becomes more negative then resting potential (hyperpolarisation). Potassium ions channels close and the resting potential is restored.
Refractory period
The period of recovery when an axon is unresponsive, this allows action potentials to be descreet events meaning they don’t merge together. There is a minimum time difference between action potentials occurring at one place on a neurone. The length of the refractory period determines the maximum frequency at which nerve impulses are transmitted.
Synapses ensure one way transmission
Impulses can only pass in one direction as neurotransmitters are released from one side of the synapse and the receptors are on the other side. It cant occur in the opposite direction.
