The nervous system Flashcards
what is the CNS made up of
The brain (85-100 billion neurones) and spinal cord (69 million neurones)
what is the PNS made up of
Cranial nerves, spinal nerves, ganglia, enteric plexus and sensory receptors in the skin
what is the enteric plexus
layers of nervous tissue that control movements in the esophagus, stomach, and intestines
what are the functions of the nervous system
-It regulates and maintains homeostasis along with the endocrine system
-It connects the entire body together and communicates using electronic impulses, which are rapid and specific and cause almost immediate responses
-The master of control and communication system of the body
-Responsible for our thoughts, feelings, behaviours, emotions, memories and initiates voluntary movement.
It makes us who we are!
the three basic functions
1
-Sensory receptors monitor changes know as stimuli.
-Gathered information is known as sensory input
2
-The CNS processes and interprets the sensory input and decides what should be done at each moment – a process called integration
3
-It then causes a response or effect by activating muscles / glands (effectors) via motor output
subdivisions of the nervous system
- Central Nervous System (CNS) “Command centres”
-Brain
-Spinal Cord - Peripheral Nervous System (PNS) - “Communicators”
-Afferent (sensory)
-Efferent (motor)
>Somatic (voluntary)
>Autonomic (involuntary) – No conscious control e.g heart
*Sympathetic
*Parasympathetic
what is a neurone
-AKA nerve cell.
-Highly specialised to transmit messages (nerve impulses) from one part of the body to another.
-Is the primary functional unit of the nervous system.
-Neurons can differ structurally but share common features.
what are dendrites
-Branch like processes that receive electrical messages and transmit these towards the cell body.
-Each neuron can have up to 100 dendrites depending on the structural type.
-These contain lots of receptors that are designed to pick up signals from other neurons that come in the form of chemicals known as neurotransmitters
what is the cell body
-AKA the “soma”
-Is the metabolic centre of the neuron.
-Contains all the usual organelles.
what is the nucleus of a neurone
-The nucleus contains the instruction of the neuron and keeps it functioning.
-Together the soma & nucleus collect the information from all the dendrites and send it through the axon hillock.
what is a axon hillock
-Cone like region of the cell body
-Gives rise to the axon.
-Acts as an “administrator”, sums up the total signals received, both inhibitory and excitatory signals. If this sum exceeds the limiting threshold, the action potential (nerve impulse) is triggered.
what is the axon
-Processes that generate nerve impulses that are conducted away from the cell body.
-Each neuron only has one axon.
-Axons can be 1mm to 1m in length.
-Axons bundled together is what makes up our nerves
what are Schwann cells
-A type of glial cell that surrounds neurons in the PNS.
-Single cells that form the myelin sheaths that wrap around a single axon.
-They play essential roles in the development, maintenance, function, and regeneration of peripheral nerves.
what are myelin sheaths
White fatty and waxy material which cover axons
Myelin protects and insulates nerve fibres and increase the speed of nerve impulse transmission.
Works like insulation in wires of an electrical cord.
what are nodes of ranvier
Because the myelin sheath is formed by many individual Schwann cells, it has gaps or indentations known as nodes of ranvier at regular intervals.
what is saltatory conduction
-Signals jump between nodes of Ranvier
-Results in faster conduction
-More energy efficient then unmyelinated nerve fibres.
-This will be explained further when we discuss action potentials in depth
nerve conduction speed
*Unmyelinated neurons:
-Speed = 0.5-10 m/s
-Equates to 1-20mph
*Myelinated neurons
-Speed = up to 150 m/s
-Equates to 335mph
what is the axon terminal
-Axon branches off at its terminal end to form (hundreds to thousands) axon terminals
-These terminals contain hundreds of tiny vesicles or membranous sacs that contain chemicals called neurotransmitters.
-When signals reach the axon terminal it stimulates the release of these neurotransmitters into the extracellular space between this neuron and its target cell. This space is known as the synaptic cleft.
-Target cells can be other neurons, muscles or glands.
what is the synaptic cleft
-Each axon terminal is separated from its target cell (in this case, a neuron) by a tiny gap called the synaptic cleft.
-Although very close, neurons and their target cells never touch
what is a synapse
-This is where a nerve impulse is transmitted to the next cell and is known as a synapse.
-Neurotransmitters are released into the cleft which travel to and then trigger an action potential in the target cell.
conductivity of a neurone
ZONE 1:
Part where incoming signals are received from other neurons
ZONE 2:
Part where action potentials are initiated
ZONE 3:
Part that conducts action potentials in an undiminishing fashion, often over long distances.
Axons can be 1mm to >1m in length.
ZONE 4:
Part that releases a neurotransmitter that influences other cells.
what is a unipolar neurone
-So named due to having a single process emerging from the cell body.
-However, it has very proximal (central) and distal (peripheral) processes
-The end of the peripheral process are dendrites which receive the signal
-The axons conduct signals both to and from the cell body (but still only in 1 direction)
-Sensory neurons in the PNS are this kind
what is a bipolar neurone
-Have 2 processes separated by a cell body
-These are very rare. Only found in special sense organs (ear nose) where they act in sensory processing as receptor cells.
what is a multipolar neurone
-Have more than two processes, a single axon and multiple dendrites
-All motor and association neurons are this kind these are the most common type of neuron
-Named due to multiple number of processes extending from the cell body.
what are neuroglial cells
-Neuroglial = “nerve glue”.
-AKA accessory or support cells.
-Account for about 50% of cellular mass of nervous system.
-Provide homeostatic support, protection, and defence to the nervous tissue.
-Different types can be found in CNS & PNS.
-Differ to neurons because they:
Do not have any synaptic contacts (do not conduct impulses).
Retain the ability to divide throughout life, particularly in response to injury.
Are much smaller than neurons
4 key areas of the brain
Cerebral hemisphere, Diencephalon, Cerebellum, Brain stem
what is the cerebral hemisphere
-AKA the “Cerebrum”
-The most superior part of the brain.
-Larger than the other 3 brain regions combined
*Splits into its own 3 regions:
-Superficial Cortex of gray matter.
-An internal white matter, and
-The basal nuclei
>The entire outer surface is covered in ridges and grooves
the frontal lobe
-Important for voluntary movement, expressive language and for managing higher level executive functions.
Contains a number of important areas…
*Motor cortex which includes:
-Primary motor cortex: (pre central gyrus)
-Premotor cortex: (anterior to primary motor cortex) Assists with planning and coordination of movement.
-Supplementary motor area (lateral and more inferiorly): programming complex sequences of movements and coordinating bilateral movements
-Frontal eye field area (superior in middle): Voluntary eye movement.
Brochas speech area (located at lateral sulcus): Articulation of speech
-Pre-frontal cortex (anterior): Plays a key role in Cognitive functions, intellect, personality and memory. -Influences attention & impulse inhibition
the parietal lobe
-Plays a vital role in sensory perception and integration. Object memory and some language.
-Primary somatosensory area (post central gyrus): Receives impulses of all receptors of somatic sensations and interprets these.
-Somatosensory association area: Sensory memory and object recognition (can tell and object with eyes closed).
-Wernicke’s area: (also into temporal lobes). Interprets the meaning of speech by recognising spoken words. If damaged more issues around word arrangement (Word salad - correct words in wrong order).
-Common integrative area: Integrates sensory stimuli and sends to other parts of brain for the appropriate response
the occipital lobe
-Mainly associated with vision: Memory, evaluation, perception and object recognition.
-Visual association area: Evaluates present and past visual experiences to evaluate what is seen (object recognition).
-Primary visual area: Visual information and perception
the temporal lobe
-It plays a key role in sensory and auditory processing, language, recognition and perception. It helps retain visual memories, and both process and remember emotions.
-Wernicke’s: Speach
-Auditory association area: Allows you to recognise a particular sounds as speech, music or noise
-Primary auditory area: receives info for sound and involved in auditory perception.
Association area / Limbic association area:
what is basal nuclei
-AKA Basal Ganglia:
-A group of sub-cortical nuclei.
-Helps initiate and terminate movement.
-Suppresses unwanted movement.
-Regulates tone.
-Damaged in Parkinson’s disease.
corpus collosum
-A large bundle of myelinated axons (white matter).
-Connects the left and right hemispheres.
-This structure allows communication of information between the left and right sides of the brain.
diencephalon
3 key structures:
Thalamus
Hypothalamus
Epithalamus
Thalamus
-Relays most of sensory information to cerebral cortex.
-Contributes to motor function by transmitting information from the cerebellum to basal ganglia to motor areas.
-Plays an important role in maintaining consciousness.
hypothalamus
-Controls and integrates activities of the ANS, endocrine system and pituitary gland.
-Regulates emotional and behavioural patterns and circadian rhythm.
-Controls body temperature.
epithalamus
Contains the:
-Pineal gland: Releases melatonin. Contributes to circadium rhythm.
-Choroid plexus: which forms cerebrospinal fluid (CSF).
what is the cerebellum
-AKA Cerebellar.
-Hindbrain structure.
-Translates from Latin to “little brain”
-Controls and refines movement, posture and balance.
-It also plays a role in other cognitive functions such as language processing and memory
what is the brain stem
Consists of 3 key structures:
Midbrain.
Pons.
Medulla oblongata.
Plays a crucial role in communication between brain and PNS.
10 of the 12 Cranial nerves originate in the brain stem
midbrain
-Contains many motor tracts that go to spinal cord (pyramidal tracts).
-Hold structures that are important for head and eye movements.
pons
-Important In maintaining respiratory regulation (coordinates RR and depth)
-Relays information from cerebrum to cerebellum
medulla oblongata
-Centre for many autonomic functions such as respiration and CV centres.
-Controls sneezing, coughing, vomiting (reflex centres)
Swallowing.
-Relays ascending sensory pathway impulses from skin and proprioceptors.
how many cervical vertebrae are there
7
how many thoracic vertebrae are there
12
how many lumbar vertebrae are there
5
how many sacral vertebrae do we have
5 (fused)
how many coccygeal vertebrae do we have
3-5 (fused)
where do the spinal cord roots branch from the vertebrae
intervertebral foreman
what happens to the nerves at the end of the spinal cord (L1-L2)
it turns from a conical or cylindrical structure to bundles of single nerves
(cauda equina)
what is the function of the spinal cord
-Provides 2 way conduction pathway to and from the brain (afferent and efferent).
-31 pairs of spinal nerves overall (C1-Cx1) that connect the CNS to the PNS.
what is the middle of the spinal cord made up of
grey matter
what is grey matter
-Neurone cell bodies
-Split into….
>Dorsal (posterior) horn - Sensory neuron axons enter spinal cord
>Ventral (anterior) horn - Motor neuron cell bodies originate.
>Lateral horn: Only exists in few thoracic and lumbar vertebrae.
what is the outer layer of the spinal cord made up off
white matter
what is white matter
-Axons of neurons.
-Where the nerve impulses are transported up and down the spinal cord
-Separated into 3 columns:
>Dorsal column.
>Ventral column.
>Lateral column
what 5 processes do all reflex arcs have
- receptor
- sensory neurone
- integration centre
- motor neurone
- effector
what is the meninges
Three layers of membranes known as meninges protect the brain and spinal cord
what are the three layers of meninges
-Dura matter (Outermost layer):
>A thick membrane made of dense irregular connective tissue that surrounds the brain and spinal cord.
-Arachnoid matter (Middle layer):
>Named due to resembling a spiders web.
>A thin, transparent membrane surrounding the spinal cord like a loosely fitting sac.
>Subarachnoid space – contains cerebral spinal fluid (CSF)
-Pia matter (Inner layer):
>Delicate connective tissue which contains many blood vessels
define decussate
Cross over
ipsilateral
same side
rostral
towards nose
afferent
Conducting or conducted inwards or towards something (to CNS)
efferent
Conducted or conducting outwards or away from something (away from CNS)
contralateral
opposite sides
somatoipcally arranged
A specific anatomical part of the body with a specific function impacting on the CNS.
what are the 2 different tracts
-Ascending tracts: which convey sensory information from receptors up to the brain.
-Descending tracts: Which convey motor output / messages to the effectors.
what are descending tracts
-Motor information / signals
Descend from brain to spinal cord
-Main role is to transmit motor signals to the effectors (muscles). 2 types
-Pyramidal: conscious control of muscles from the cerebral cortex to the muscles of the body and face; and
-Extrapyramidal: unconscious, reflexive or responsive control of muscles from various brainstem structures to postural or anti-gravity muscles.
what are ascending tracts
-Sensory information / signals
Ascend from spinal cord and connect it to brain
-Main role is transmit 2 types of somatosensory information:
-Exteroceptive: comes from the body’s exterior, such as pain, temperature, touch and pressure.
-Proprioceptive: comes from the inside the body, such as muscles and joint receptors.
what happens at the stimulus part of an impulse/AP
Stimulus - this excites the neurone cell membrane, causing sodium ion channels to open. The membrane becomes more permeable to sodium, so sodium ions diffuse into the neurone down the sodium ion electrochemical gradient. This makes the inside of the neurone less negative.
what happens at the depolarisation part of an impulse/AP
if the potential difference reaches the threshold (around -55 mV), more sodium ion channels open. More sodium ions
diffuse rapidly into the neurone.
what happens at the repolarisation part of an impulse/AP
at a potential difference of around +30 m the sodium ion channels close and potassium ion channels open. The membrane is more permeable to potassium so potassium ions diffuse out of the neurone down the potassium ion
concentration gradient. This starts to get the membrane back to its resting potential.
what happens at the hyper polarisation part of an impulse/AP
potassium ion channels are slow to close so there’s a slight ‘overshoot’ where too many potassium ions diffuse out of the neurone. The potential
difference becomes more negative than the resting potential (i.e. less than -70 mV).
what happens at the resting potential part of an impulse/AP
the ion channels are reset. The sodium-potassium pump returns the membrane
to its resting potential and maintains it until the membrane’s excited by another stimulus.
what is saltatory conduction
-Signals jump between
Nodes of Ranvier
-Results in faster
conduction
-More energy efficient as
less depolarization occurs
(only at nodes of Ranvier)
and less sodium potassium
pumps working
what is the corticospinal tract
-Control of:
> Voluntary
> Discrete
> Skilled movement
-LATERAL CST
>Fine and skilled motor
movement
-ANTERIOR CST
>Gross, axial motor movement
what is the vestibulospinal tract
-Originates in medulla
-MEDIAL –head/neck musculature
-LATERAL – extensors/ antigravity musculature of limb and trunk
-Helps maintain posture and balance
what is Pontine Reticulospinal tract (RST)
-Activating EXTENSOR muscles (like VST)
-Acts more as an assistor to the activation of extensor musculature
-Combine with VST –
They are VERY PRETTY
VST Pontine Reticulospinal Tract
-Majority of tract is ipsilateral
what is the medullary reticulospinal tract
-Lateral (Medullary)
-Bilateral, although mainly ipsilateral
-Inhibitory to spinal and cranial alpha motor neurons
-Again influences muscle spindle
-Allows selective flexion of limbs to allow functional activity eg/
stepping/hand to mouth
-Tone is reduced to axial & proximal musculatur
what is the corticobulbar tract
-Arise from lateral aspect of PRIMARY MOTOR CORTEX
-Receives same inputs as corticospinal tracts
-Fibres converge passing through INTERNAL CAPSULE of brainstem
-Neurones terminate on MOTOR NUCLEI of CRANIAL NERVES in BRAIN
STEM, synapsing with LMN
-LMN carry motor signals to muscles of face and neck
what is rubrospinal tract
-Function is FLEXION of UL, but keeps flexors of LL in check
-Originates in RED NUCLEUS of midbrain
-Input from CEREBELLUM (globus nuclei and emboliform nuclei) and from CORTEX (corticorubral fibres)
