Nervous system main Flashcards
(26 cards)
Neuron: Cell body
Biosynthetic centre and receptive region. Contains usual organelles
Most neuron cell bodies are located in CND where they are protected.
Cluster of cell bodies in the CNS= nuclei
Cell bodies that lie along nerves in PNS = ganglia
Neurons: Dendrites
Motor Neurons have hundreds clustered close to cell body
Main receptive and input regions
Provides enormous surface for receiving signals
Convey incoming messages to cell body
Neurons: Axon
Conducting region of neuron
In some it is very short others it accounts for nearly entire length of neuron
Generates nerve impulses and transmits them away from cell body
Impulse reaches axon terminals causing neurotransmitters to be released
Each neuron both receives signals from and sends signals to scores of others
Carries messages from many different Neurons at same time.
Decay quickly if damaged.
Neuron Functional Classification
Sensory (afferent) : transmit impulses from sensory receptors in skin or internal organs towards CNS. Virtually all are uni polar; cell bodies located in sensory ganglia outside CNS
Motor (efferent) carry impulses away from the CNS to the effector organs (muscles and glands)
Mainly multi polar; cell bodies located in CNS
Interneurons: lie between sensory and motor.
Most confined to CNS
Make up 99% of Neurons in body.
Mostly multipolar
Nerve Impulse Resting stage
Electrical difference across membrane in axon is called its resting membrane potential. (Negative inside positive outside.
resting potential achieved by sodium potassium pump. Moves more Na+ outside then K+ inside causing the cell to be more positive outside then inside.
Nerve Impulse: Depolarization
Stimulus causes sodium channels in membrane to open allowing Na+ to flow in.
Gated ion channels in membrane open and close to signals like electrical charges
When Na+ enters the neuron the cells electrical potential becomes more positive.
If signal is strong enough and reaches a threshold it triggers the action potential.
More gated channels open allowing more Na+ inside and the cell depolarises so that the charges across membrane completely reverse.
(Cell becomes more positively charged and outside more negatively.
This action potential will then travel down the axon as more na channel open
Peak voltage of AP= sodium channels close and potassium open.
K+ moves out and Na+ stays inside the membrane repolarizing the cell.
(Hyperpolarized)
K+ gates then close. More K outside than it has Na inside. Cells potential is than lower than resting potential.
Nerve Impulse: Repolarization.
Neuron enters a refractory period which returns potassium inside of the cell and sodium to the outside via the sodium potassium pump
Returns to normal polarized resting state.
CNS Protection: Bones
Outermost protective layer.
Brain is protected by cranium
Spinal cord by the opening in the vertebrae (vertebral canal)
CNS Protection: Meninges
Protect tissue of the brain and spinal cord and help hold them in place
3 layers:
Outer: tough fibrous and sticks to the skull (less fitting in vertebral column)
Middle: loose mesh fibres to hold brain in position
Inner: very delicate and contains blood vessels. Sticks closely to brain and spinal cord.
CNS Protection: Cerebrospinal fluid (CSF)
Clear watery fluid containing some cells glucose protein urea and salts.
Produced by choroid plexus nerve complex in the brain.
Occupies space between middle and inner meninges
acts a shock absorber and supports the brain.
Circulates CNS and eventually re-enters the blood capillaries.
during circulation takes nutrients and carries away waste from CNS
CNS: Matter
White: part of the brain and spinal cord made up of myelinated fibres
Grey: nerve cell doors and unmyelinated fibres.
Cerebellum: outer fold is grey and inner branches are white.
Cerebrum: surface is grey and deep inside. In between is two zones of white
Nerve Transmission: Synapse
Action potential arrives at axon terminal.
Voltage calcium ion channels open and Ca2+ enters axon terminal.
Entry of Calcium causes vesicles in synapse to release neurotransmitters by exocytosis.
Neurotransmitter diffuses across synaptic cleft and binds to specific recoveries in membrane of post-synaptic neurone dendrites.
Binding of neurotransmitter opens ion channels resulting in graded potentials (if excitory)
Neurotransmitters effects terminated by reuptake back into axon terminal, broken down by enzymes or diffusion away from synapse
Cerebrum
3 Functional Areas:
Sensory: receive and process nerve impulses from the senses
Motor: send impulses to muscles, especially for voluntary movement.
Association: interpret information from the senses and mKe it useful (concerned with intellectual and emotional processes)
Cerebellum
Receives signals from motor areas of the cerebral cortex as well as other sensory signals and compares them.
Inner ear (posture and balance). Stretch receptors in skeletal muscle
Corrective feedback to the motor neurons in the cerebral cortex.
Exercises control over posture balance and fine coordination of voluntary muscle movement.
Medulla Oblongata
Important role in automatically adjusting body functions.
Cardiac Centre: regulates the rate and force of heartbeat.
Respiratory Centres: which control rate and depth of breathing.
Vasomotor Centre: regulates the diameter of blood vessels.
Control of Body temperature
Thermoregulation
Peripheral thermoreceptors in skin and mucous membranes - send information to hypothalamus
Central thermoreceptors located in hypothalamus
Stimulus: change in temperature
Receptor: thermoreceptors (skin or in hypothalamus)
Modulator: thermoregulatory centre in medulla Oblongata
Autonomic nervous system
Effector: (increase in temp) sweat glands or peripheral arterioles
Response: sweating and vasodilation
Feedback: decrease in body temp. Increase in heat loss
Summary of thermoregulatory mechanisms
> 38*C. Increase heat loss via sweating and vasodilation.
Heart Rate regulation: NODES
sinoatrial node (SA node) rythmical contractions of the heart. Wall of right atrium.
Atrioventricular Node(AV node) Located between the two atria near valves.
Heart Rate Regulation: Heartbeat
SA node sends out nerve impulses that spread through atria
Stimulus reaches the AV node. At about this time contraction of the muscle of the atrium begins.
Stimulation of the AV node causes it to send out its own impulse. These travel down the fibres in the septum between the ventricles.
Impulses then spread out through the muscles of the ventricles. Atrial contraction is now complete and ventricular contraction begins.
Heart Rate Regulation: Autonomic influence
Sympathetic: sympathetic nerve fibres from cardiac regulating centre connect to both nodes. These sympathetic fibres release the neurotransmitter
Noradrenaline= increase in heart rate and stroke volume.
Parasympathetic: impulses from parasympathetic nerves causes the release of acetylcholine= decrease in heart rate and stroke volume.
Rest= parasympathetic neurons are dominant
Exercise= increase in activity of sympathetic neurons and decrease in activity of parasympathetic. =increase in heart rate.
Heart Rate regulation: Receptors and feedback
Pressoreceptors(baroreceptors) respond to changes in blood pressure and send messages to cardiac regulating centre (medulla Oblongata)
Stimulus: change in blood pressure
Receptor: baroreceptors
Modulator: cardiac centre (medulla Oblongata)
autonomic nervous system.
Effector: SA/AV
Response: Sympathetic: increase heart rate and stroke volume
Parasympathetic: decrease heart rate and stroke volume.
Control of Breathing: Receptors
Chemoreceptors respond to changes in Oxygen levels and H+ levels.
Central: located throughout the brain.
Peripheral: found in aortic arch and carotid arteries.
Control of Breathing: Carbon dioxide
CO2 levels rise and are hydrated to form carbonic acid
Carbonic acid dissociates and releases H+ = drop in pH.
Increase in H+ excited central chemoreceptors.
They make many synapses with the respiratory regulatory centre in the medulla oblongata.
Stimulates the diaphragm and intercostal muscles. Increases breathing rate and depth of breath.
Control of Breathing: Oxygen
Peripheral chemoreceptors contain cells sensitive to arterial O2 receptors
Arterial oxygen levels must drop significantly to become major stimulus for increased ventilation. (Large reservoir of O2 bound to haemoglobin which remains saturated until Oxygen levels drop dramatically)
