5.1 - Communication and Homeostasis

What is a response?

A behavioural or physiological change in an organism as a result of a stimulus.

What is a stimulus?

A change in the internal or external environment of an organism.

What is homeostasis?

Responses that maintain a constant internal environment inside an organism.

Name 4 internal conditions that are maintained by an organism's homeostasis.

Body temperature, blood glucose concentration, blood water potential, carbon dioxide concentration.

Put the following aspects of a feedback mechanism in order: processor, stimulus, effector, response, receptor.

Stimulus, receptor, processor, effector, response.

What are the 2 communication systems in mammals?

Nervous, hormonal.

What is cell signalling?

The release of a chemical from a cell that is complementary to a receptor in a target cell, bringing about a response in the target cell.

What is an effector?

A cell or tissue that brings about a response to a stimulus.

What are the 3 types of effector?

Muscle cell, gland cells, liver cells.

What is meant by the potential difference across a membrane?

The difference in potential between inside and outside the cell.

What is meant if a membrane is polarised?

The inside of the cell has a more negative potential than outside.

What is the resting potential value of a resting neurone?

-60mV.

What 3 things maintain the resting potential of a resting neurone?

Presence of large organic anions inside the cell, 3 Na+ out, 2 K+ in by Na+/K+ pump, membrane is more permeable to K+.

Where is the highest concentration of Na+ at resting potential?

Outside the cell.

Name 3 types of neurone.

Motor, sensory and relay.

Describe the structure and function of a motor neurone.

Their cell body is located in the CNS and they have a long axon carrying the action potential to the effector.

Describe the structure and function of a sensory neurone.

Have a long dendron carrying the action potential from a sensory receptor to the cell body, positioned outside the CNS. They have a short axon carrying the action potential into the CNS.

Describe the structure and function of a relay neurone.

They connect the sensory and motor neurones in the CNS. They have short dendrites and short axon.

What is meant by a myelinated neurone?

The neurone is insulated by a myelin sheath, which is Schwann cells wrapped tightly around the neurone.

Describe any advantages of myelination of neurones.

An action potential can be transmitted much quicker as the signal jumps between the nodes of Ranvier.

Where are non-myelinated neurones found?

They are often used to coordinate body functions such as breathing or digestion, carrying action potentials over shorter distances.

What is a sensory receptor?

A cell or tissue that monitors an aspect of an organism's internal or external environment.

What do sensory neurones do?

They convert the energy of a stimulus into electrical energy.

Name 6 examples of sensory receptors.

Thermo, chemo, baro, photo, proprio, osmo.

Sensory neurones act as a transducer. What is a transducer?

Something that converts one form of energy into another.

What is a processor?

A tissue or organ that coordinates the input from sensory receptors and communicates the output response to the relevant effector.

What is a Pacinian corpuscle?

A pressure sensor that detects changes in pressure or vibration in the skin.

Describe the structure of a Pacinian corpuscle.

The corpuscle is oval shaped with a series of rings of concentric connective tissue, wrapped around the end of a nerve cell.

How does a Pacinian corpuscle detect pressure changes?

The corpuscle is sensitive to changes in pressure that deform the rings of connective tissue. Therefore, no response occurs when the pressure is constant.

How are cell membrane proteins involved in neural communication?

Some proteins are channels allowing the movement of ions across the membranes by facilitated diffusion, while others are transport proteins that actively move ions across the membrane requiring energy in the form of ATP.

What happens if a stimulus is too weak?

The generator potential will not reach the threshold level and so there is no action potential.

Where is the highest concentration of K+ at resting potential?

Inside the cell.

Describe how a sodium/potassium pump in the cell membrane functions.

3 Sodium ions are actively pumped out of the cell, with 2 potassium ions going into the cell.

What is meant if a membrane depolarises?

The inside of the cell has a less negative potential than outside.

What causes a membrane to depolarise?

Some Na+ channels open, allowing Na+ to diffuse down its concentration gradient.

What happens in the neurone membrane if threshold potential is reached?

Voltage-gated Na+ channels open for a bigger influx of Na+.

What is the action potential value of a stimulated neurone?

#ERROR!

What happens in the neurone membrane at +40mV?

Voltage-gated Na+ channels close, and voltage-gated K+ channels open.

What is repolarisation?

Return of membrane potential difference to more negative inside the cell than outside.

What causes repolarisation?

Diffusion of K+ out of the cell down their concentration gradient.

What is hyperpolarisation?

Overshoot of membrane potential difference so that inside is more negative than outside than at resting potential.

What happens in the neurone membrane at -70mV?

Voltage-gated K+ channels close.

What causes hyperpolarisation?

Voltage-gated K+ channels only close at -70mV so K+ continues to diffuse out of the cell.

What is the refractory period?

A short period of time after an action potential when it is impossible to stimulate the membrane into another action potential.

What are the 2 purposes of the refractory period?

To restore the resting potential Na+/K+ concentrations on either side of the membrane, to ensure action potentials only transmit in one direction.

What is a local current in a neurone?

Diffusion of Na+ from point of entry to area of low concentration adjacent to the next region of membrane.

What is an electrochemical gradient?

A concentration gradient of ions.

What is saltatory conduction in a neurone?

Elongated local currents in myelinated neurones so that action potentials only occur at nodes of Ranvier.

How does changing the intensity of the stimulus affect the action potential?

Makes them more frequent.

What is a synapse?

A junction between 2 or more neurones.

What is a synaptic cleft?

A small gap between 2 neurones.

What is a neurotransmitter?

A chemical released from the pre-synaptic neurone that causes a new action potential in the post-synaptic neurone.

What are 4 examples of neurotransmitters?

Acetylcholine, adrenaline, dopamine, GABA.

Name one example of an excitatory neurotransmitter.

Acetylcholine.

Name one example of an inhibitory neurotransmitter.

GABA.

What is the difference between excitatory and inhibitory neurotransmitters?

Excitatory: causes depolarisation of postsynaptic neurone, causes action potential to be triggered; Inhibitory: causes hyperpolarisation of postsynaptic neurone, prevents action potential to be triggered.

What is a cholinergic synapse?

A synapse that uses acetylcholine as a neurotransmitter.

What are the 4 specialisations of the pre-synaptic bulb?

Many mitochondria, complex SER, many vesicles containing neurotransmitter, voltage-gated Ca2+ channels.

What is the specialisation of the post-synaptic membrane?

Neurotransmitter-gated Na+ channels.

What is acetylcholinesterase?

Enzyme that hydrolyses acetylcholine into acetic acid and choline.

What is the "all or nothing" principle?

Each action potential is the same size and intensity.

What is an excitatory post-synaptic potential (EPSP)?

A small depolarisation in the post-synaptic neurone caused by a small number of neurotransmitter molecules being released from the pre-synaptic neurone.

What is summation?

The reaching of threshold potential in the post-synaptic neurone due to the combination of several EPSPs.

What is temporal summation?

The reaching of threshold potential in the post-synaptic neurone due to the combination of several EPSPs consecutively from the same pre-synaptic neurone.

What is spatial summation?

The reaching of threshold potential in the post-synaptic neurone due to the combination of several EPSPs from several different pre-synaptic neurones.

What is an inhibitory post-synaptic potential (IPSP)?

A small hyperpolarisation in the post-synaptic neurone caused by a small number of neurotransmitter molecules being released from the pre-synaptic neurone.

What are the 2 divisions of the nervous system?

Central, peripheral.

What are the 2 organs of the central nervous system?

Brain, spinal cord.

What organ connects the central and peripheral nervous systems?

Spinal cord.

What type of neurones is the brain mostly composed from?

Relay.

What are the 2 divisions of the peripheral nervous system?

Sensory, motor.

What are the 2 divisions of the motor nervous system?

Somatic, autonomic.

What is the function of the somatic nervous system?

Conduct action potentials to effectors that are under voluntary / conscious control.

What are 2 structural features of the somatic nervous system?

Mostly myelinated neurones, single neurone connects CNS to effector.

What effectors are controlled by the somatic nervous system?

Skeletal muscles.

What is the function of the autonomic nervous system?

Conduct action potentials to effectors that are not under voluntary / conscious control.

What are 3 structural features of the autonomic nervous system?

Mostly non-myelinated neurones, at least 2 neurones connect CNS to effector, connections between neurones called ganglia.

What 3 effectors are controlled by the autonomic nervous system?

Smooth muscle, glands, cardiac muscle.

What are the 2 divisions of the autonomic nervous system?

Sympathetic, parasympathetic.

What is the function of the sympathetic nervous system?

Prepare the body for activity.

What is the function of the parasympathetic nervous system?

Conserve energy.

What are 3 effects of the sympathetic nervous system being more active than the parasympathetic nervous system?

Increased heart rate, increased ventilation rate, decreased digestion.

What are 3 effects of the parasympathetic nervous system being more active than the sympathetic nervous system?

Decreased heart rate, decreased ventilation rate, increased digestion.

What are 3 structural features of the sympathetic nervous system?

Ganglia close to CNS, 1:1 nerve:effector ratio, acetylcholine as neurotransmitter.

What are 3 structural features of the parasympathetic nervous system?

Ganglia close to effector, 1:many nerve:effector ratio, noradrenaline as neurotransmitter.

What are the 4 main regions of the brain?

Cerebrum, cerebellum, hypothalamus / pituitary complex, medulla oblongata.

What is the function of the cerebrum?

Coordinates higher functions such as conscious thought & actions, emotions, speech and memory.

What part of the brain connects the 2 cerebral hemispheres?

Corpus callosum.

What are the 4 lobes of the cerebrum?

Frontal, parietal, temporal, occipital.

What are the 3 areas found in each lobe of the cerebrum?

Sensory, association, motor.

What is the function of the cerebellum?

Coordinates balance and fine movement control.

What part of the brain connects the cerebellum to the cerebrum?

Pons.

What is the function of the hypothalamus / pituitary complex?

Coordinates homeostatic mechanisms such as thermoregulation and osmoregulation.

What is the function of the medulla oblongata?

Coordinates physiological processes such as heart rate, blood pressure and ventilation rate.

What is a reflex action?

A response that requires no processing from the brain.

What are 2 examples of a reflex action?

Blinking, knee jerk.

What is a cranial reflex?

A reflex action with a nervous pathway through the brain.

What is a spinal reflex?

A reflex action with a nervous pathway through the spinal cord.

What does a corneal reflex do?

A reflex action with a nervous pathway through the brain, causing the eyelid to blink.

What part of the medulla oblongata controls heart rate?

Cardiovascular centre.