The nervous system Flashcards
Diagram to show structure of the nervous system
function of the nervous system
detect and respond to changes inside and outside of the body
two types of nervous tissue
neurones
neuroglia
neurones function
to generate anf transmit nerve impulses
what do neurones consist of?
Cell body and it’s processes: one axon and usually many dendrites
neurones are different structures depending on it’s function
Structure of the different neurones
what is an Action potential?
electrical impulse transmitted by neurons
what stimilis can action potentials be initiated in response from?
outside the body - eg. touch, light waves
inside the body - eg. change in the concentration of CO2 in the blood alters respirationm, a thought may result in voluntary movement
Relay neurones
a neurone which recieves an action potential, passes it on or sometimes redirect it. (short axon). only found in CNS.
interneurons
Carry electrical impulse from sensory neuron to motor neuron. only found in CNS.
why do neurons need a continuous supply of oxygen and glucose?
as they can’t divide. unlike many other cells, neurons can normally synethise chemical energy (ATP) only from glucose.
Cell bodies
form the grey matter of the nervous system. found in the periphery of the brain and in the centre of the spinal cord. Group of cell bodies are called the nuclei in the CNS and ganglia in the PNS.
Axon and dendrites
extensions of cell bodies and form the white matter of the nervous system. axons are found deep within the brain and in groups, called tracts, at the periphery of the spinal cord. They are referred to as nerves or nerve fibres outside the brain and spinal cord.
Axon
carry impulses away from the cell body and are usually much longer than the dendrites.
multipolar neuron
a type of neuron that possesses a single axon and many dendrites (and dendritic branches). the most common type of neuron. They are located in the central nervous system (brain and spinal cord) and in autonomic ganglia.
bipolar neuron
a neuron with only two extensions—an axon and a dendrite—that run from opposite sides of the cell body. Cells of this type are found primarily in the retina
unipolar neuron
the simplest class of neurons that exhibit a single extension that gives rise to branches, some of which are receptive (dendrites). they are located within the skin, joints, muscles, and internal organs.
schwann cell
nucleus of schwann cell is found on the axon of myelinated neurones. it produced myelin sheath.
Dendrites
many short processes that recieve and carry incoming action potentials towards cell bodies.
in Motor Neurons they form part of the synapses
in sensory neurons they form the sensory receptors that respond to specific stimuli
how does an Action potential travel through a neuron
There’s already a resting membrane potential between the outside (positive) and the inside of the neuron (negative). When the action potential enters the cell, it causes the sodium channels to open, which cause Na+ to enter the cell, which depolarises the cell. This causes the action potential to conduct along the axon. After the action potential is conducted along the axon K+ leaves the neurone to repolarise the cell and to restore the resting membrane potential.
Travel of Action potential diagram
Refractorary period
The neuron hyperpolarises to allow the neuron to restore membrane potential before allowing any other action potentials to be generated.
Saltatory conduction
in myelated neurones where the movement of ions across the membrane can only occur at the nodes of ranvier (where there is no myelin sheath), which causes the conduction of the action potential to ‘jump’ along the axon, which is a quicker conduction compared to no mylenated neurons.
Synapse process
the electrical action potential reaches the pre-synaptic bulb which causes the voltage gated calcium channels to open and allow ca2+ ion to enter. This causes vesicles containg chemical neurotransmitters to fuse with the membrane and leave the neuron and enter the synaptic cleft. via diffusion the neurotransmitters bind to receptors on the post-synaptic bulb and causes ligand gated sodium channels to open. this allows Na+ ions to enter the cell, causing the neuron to depolarise and generate an action potential.
synapse diagram
what are the three proctetive connective tissues?
Endoneurium
Perineurium
Epineurium
diagram of the protective connective tissues
Endoneurium
delicate tissue surrounding each individual fibre (chain of neuron)
Perineurium
smooth connective tissue surrounding each bundle of fibres
Epineurium
fibrous tissue surrounding and enclosing a number of bundle of nerve fibres. Most large nerves are covered by epineurium.
sensory (afferent nerves) function
carry information from the body to the spinal cord.
sensory receptors
specialised endings of sensory neurones respond to different stimili inside and outside the body
Somatic, cutaneous or common senses
originate from the skin. pain touch heat and cold
proprioreceptor senses
originate in the muscle and joints. they send information to the brain about the position of the body and it’s parts in space, enabling maintenance of posture and balance.
special senses
hight, hearing, balance, smell and taste
autonomic afferent nerves
originate in internal organs, glands and tissues e.g. the baroreceptoes involved in the control of BP. and the chemoreceptors involved in the control of respiration and are associated with reflex regulation of involuntary activity and visceral pain.
Motor / efferent nerves
originate in the brain, spinal cord and autonomic ganglia. they transmit impulses to the effector organs: muscles and glands.
what are the two types of motor nerves?
somatic nerves - involved in volunatary and reflex skeletal muscle contraction
autonomic nerves (sympathetic and parasympathetic) - involved in cardiac and smooth muscle contraction and glandular secretion, all involuntary functions.
mixed nerves
this is where outside the spinal cord called sensory and motor nerves are enclosed within the same sheath of connective tissue, compared to in the spinal cord where they’re enclose in separate tracts.
Autonomic motor cells
sympathetic (adrenergic and cholinergic) and parasympathetic
Sympathetic nervous system
fight or flight
parasympathetic nervous system
rest and digest (involuntary)
neuroglia
general term to describe the four glia cells. all can replicate throughout life.
what are the 4 neuroglia cells?
Astrocytes
oligodendrocytes
ependymal cells
microglia
Astrocytes
most abudant neuroglia. Blood is separated from the neurones by the capillary wall and a layer of astrocyte foot processes which form together the blood brain barrier.
blood brain barrier
a selective barrier that protects the brain from potentially toxic substances and chemical variations in the blood. eg. after a meal O2, C02, glucose and other lipid-soluble substances, such as alcohol quickly pass the barrier into the brain. some large molecules, many drugs, inorganic ions and amino acids pass more slowly or don’t pass at all, from the blood to the brain.
Oligodendrocytes
smaller than astrocytes. found in clusters round nerve cell bodies in grey matter and are located adjacent to and along the length of myelinated nerve fibres. They form and maintain myelin in the CNS and myelanate many cells at once, whereas schwann cells in the PNS can only myleanate one cell at a time.
Ependymal cells
forms the epithelial lining of the ventricles of the brain and central canal of the spinal cord. they’re part of the choroid plexuses. some also have cilia that assist the floe with the CSF.
Microglia
least abundant glia cells. they are dispersed throughout the brain and migrate to become phagocytocytic, removing microbes and damaged tissue, in areas of inflammation and cell destruction.
What can cause damage to neurones? (7)
hypoxia (lack of oxygen to tissue) and anoxia (no oxygen at all)
nutritional deficiencies
poisons e.g. organic lead
trauma
infections
ageing
hypoglycaemia (low blood glucose)
what to astrocytes do when their cells are damaged?
Their processes multiple forming a mesh (‘scar’) around the damaged CNS neurones, inhibiting the regrowth of them
what do oligodendrocytes do when they are damaged?
they increase in number round the degenerating neurones and are destroyed in demylinating diseases such as multiple sclerosis
What do microglia do when they are damaged?
when there’s inflammation and cell destruction, they are activted and migrate to site of damage, and become phagocytic. this occurs in diseases such as MS, alzheimers and strokes
What makes up the central nervous system?
the brain and spinal cord
what protects the CNS?
Skull - brain
Vertebrae - spinal cord
meninges - provide further protection for both
Meninges
membrane covering consisting of three layers of tissue, lying between the skull and brain and between the verterbral foramina and the spinal cord to provide protection.
three layers of the mininges
dura mater
arachnoid mater
pia mater
the two spaces associated with the miniges in the brain
the subdural space
the subarachnoid space
the three spaces associated with the meninges in the spinal cord
the subdural space
the subarachnoid space
the epidural space (additional space in the spinal cord compared to brain)
Dura matter
consists of 2 layers of fibrous tissue. at certain points of the brain the two layers have space inbetween them that has dural venous sinus that venous blood from the brain drains into.
what are the two layers of the dura matter?
periosteum dura
meningeal dura
periosteum dura matter
outer layer of dura matter on the inner surface of the skull bones
meningeal dura matter
inner layer of dura mater provides a protective covering of the brain.
where does the two layers of dura matter connect after separating in the brain?
falx cerebri
tentorium cerebelli
what does the dura mater do?
provides protection of the brain and ensures all structures structures stay in place
arachnoid mater
layer of fibrous tissue that protects the brain and spinal cord from sudden impact. it’s lies between the dura matter (separated by the subdural space) and the pia mater (separated by subdural space, ehich contains cebrospinal fluid CSF). it accomanies the layers of the dura mater to create the falx cerebri and tentorium cerebeli.
pia mater
the innermost layer of the meninges. It is a delicate layer of connective tissue containing many minute blood vessels.closely covers the brain. It acts as a barrier and aids in the production of cerebrospinal fluid.
what are the four ventricles of the brain
right and left lateral ventricles
third ventricle
fourth ventricle
they are all irrelegular-shaped cavities
function of the brian ventricles
to produce and secrete cerebrospinal fluid to protect and maintain your central nervous system
lateral ventricles
these cavities lie within the cerebral hemispheres, 1 each side of the median plane just below the corpus callosum. they are separated by a thin membrane called the septum lucidum and are lined with ciliated epithelium.
interventricular foramina
opening between the lateral ventricles and the third ventricle, which allows cerebrospinal fluid to pass between them and communication to occur.
third ventricle
a cavity situated below the lateral ventricles between the two parts of the thalamus. it communicates with the fouth ventricle by a canal called the cerebral aqueduct.
The cerebral aqueduct
a channel that connects the third ventricle with the fourth ventricle and allows cerebrospinal fluid to pass between them.
fourth ventricle
diamond shaped cavity located below and behind the third ventricle between the cerebellum and pons. it’s continuous below the central canal of the spinal cord and communicates with the subarachnoid space by foramina in it’s roof. CSF enters the subarachnoid through these opening.
Diagram of the brains ventricles
Cerebrospinal fluid
circulates constantly from the ventricles through the subarachnoid space around the brain and spinal cord. It is a clear, slightly alkaline fluid with a specific gravity of 1.005. continually produced and flowing.
it consists of:
water
mineral salts]glucose
plasma proteins (small amount of albumin and globulin)
a few leukocytes
small amounts of creatinine
small amounts of urea
CSF Functions
supports and protects the brain and spinal cord by maintaining a uniform pressure around these vital structures and by maintaining uniform pressure around these vital structures. acts as a cushion or shock absorber between the brain and the skull.
keeps brain and spinal cord moist and is involved in regulation of breathing as it bathes the surface of the medulla.
choroid plexuses
secretes CSF into each of the 4 brain ventricles. theses are vascular areas that are rich in blood vessels and surrounded by ependymal cells in the lining of the ventricle walls.
What does CSF pass back into the blood through?
tiny finger-like projections of arachnoid mater, called arachnoid villi, which project into the venous sinuses.
how is the movement of CSF from the subarachnoid space to venous sinuses controlled?
by difference in pressure each side of the walls of the arachnoid villi, which act as one way valves. when pressure of CSF is higher than the venous pressure , CSF is pushed into the blood and vice versa. when venous pressure is higher the arachnoid villi collapse, preventing the passage of blood constituents into the CSF. there may also be some reabsorption of CSF by cells in the walls of the ventricles.
How does CSF flow from the roof of the fourth ventricle into the subarachnoid space?
CSF flows through foramina into the subarachnoid space and completely surrounds the brain and spinal cord. its movement is aided by pulsating blood vessels, respiration and changes of posture.
parts of the brain (7)
cerebrum
thalamus
hypothalumus
midbrain
pons
medulla oblongata
cerebellum
Diagram to show structure of the brain
cerebrum
the uppermost part of the brain. It contains two hemispheres split by a central fissure. The cerebrum itself contains the major lobes of the brain and is responsible for receiving and giving meaning to information from the sense organs, as well as controlling the body. initiates and coordinates movement and regulates temperature. Other areas of the cerebrum enable speech, judgment, thinking and reasoning, problem-solving, emotions and learning. Other functions relate to vision, hearing, touch and other senses.
cerebral cortex
the outermost layer of the brain that is associated with our highest mental capabilities. The cerebral cortex is primarily constructed of grey matter. is associated with higher level processes such as consciousness, thought, emotion, reasoning, language, and memory
diencephalon
connects the cerebrum and the midbrain.thalamus and hypothalamus are sitiuated here.
thalamus
mostly gray matter structure of the diencephalon. The thalamus is composed of different nuclei that each serve a unique role, ranging from relaying sensory and motor signals, as well as regulation of consciousness and alertness.
hypothalamus
controls your hormone system. It releases hormones to another part of your brain called the pituitary gland, which sends hormones out to your different organs
mid brain
also called mesencephalon, region of the developing vertebrate brain that is composed of the tectum and tegmentum. The midbrain serves important functions in motor movement, particularly movements of the eye, and in auditory and visual processing.
pons
part of a highway-like structure between the brain and the body known as the brainstem. The brainstem is made up of three sections, and carries vital information to the body. The pons relays information about motor function, sensation, eye movement, hearing, taste, and more
medulla oblongata
lays a critical role in transmitting signals between the spinal cord and the higher parts of the brain and in controlling autonomic activities, such as heartbeat and respiration
cerebellum
s important for making postural adjustments in order to maintain balance. Through its input from vestibular receptors and proprioceptors, it modulates commands to motor neurons to compensate for shifts in body position or changes in load upon muscles.
grey matter
serves to process information in the brain. The structures within the grey matter process signals from the sensory organs or from other areas of the grey matter. This tissue directs sensory stimuli to the neurons in the central nervous system where synapses induce a response to the stimuli.
white matter
the tissue through which messages pass between different areas of grey matter within the central nervous system. The white matter is white because of the fatty substance (myelin) that surrounds the nerve fibers (axons).
functions in affecting learning and brain functions, modulating the distribution of action potential, and coordinating communication between the different brain regions
grey matter and white matter in the spinal cord diagram
Reflex arc
a neural pathway that controls a reflex. In vertebrates, most sensory neurons do not pass directly into the brain, but synapse in the spinal cord. This allows for faster reflex actions to occur by activating spinal motor neurons without the delay of routing signals through the brain.
