nervous system Flashcards
where is gray matter located in the brain?
- on the outer layer
- has the cell bodies
where is white matter located in the brain?
on the inner layer
where is gray matter located in the spinal cord?
inner layer
where is white matter located in the spinal cord?
outer layer
are myelinated or unmyelinated axons in the gray matter?
unmyelinated axons
are myelinated or unmyelinated axons in the white matter?
myelinated axons
white from colour of myelin sheath
what seperates the frontal lobe from the temporal lobe?
the lateral sulcus
what is the corpus callosum?
the white matter tract that connects the two hemispheres of the brain
what is the longitudinal fissure?
- runs the length of the brain and seperates the two hemispheres
- a deep groove that marks the division between the left and right cerebral hemispheres of the brain
what is the name for the two hemispheres of the brain?
the cerebrum
what does the central nervous system include?
- brain
- spinal cord
what does the peripheral nervous system include?
- motor
- sensory
what are CNS components encased by?
bone:
- brain within the skull
- spinal cord within the vertebral column
why are CNS components encased by bone?
for protection
lissencephalic
smooth
gyrencephalic
grooved (increased surface area)
what are the grooves in the brain called?
sulci
what are the ridges in the brain called?
gyri
what are the lobes of the cerebral cortex?
- frontal lobe
- parietal lobe
- temporal lobe
- occipital lobe
what is the cerebral cortex?
- outer layer that lies on cerebrum
what is the cerebrum?
- the largest part of the brain
- divided into two halves = cerebral hemispheres
rostral
directed towards the nose / to the front
caudal
directed towards the tail / to the back
what does the central sulcus do?
seperates frontal and parietal lobes
what does the lateral sulcus do?
seperates frontal and parietal lobes from temporal lobe
(sylivain fissure)
where is the parieto-occipital sulcus?
between the parietal and occipital lobes
where is the calcarine sulcus?
within the occipital lobe (primary visual cortex)
cerebellum
- little brain
- controls movement and coordination
- large surface areas
- densely packed with neurons
how many lobes does the cerebellum have?
3 = anterior, posterior, flocculonodular
the brainstem
- regulates vital body functions (breathing, body temp, consciousness, sleep/wake cycle…)
- can be seperated into midbrain, pons and medulla oblongata
midbrain
- vision
- hearing
- motor control
- needed as a “relay center”
pons
- pneumotaxic centre
- unconscious processes and jobs e.g. sleep/wake cycle, breathing
medulla oblongata
- cardiac
- respiratory
- vasomotor
- vomiting (can detect chemoreceptors)
cerebral ventricular system
- 4 interconnected cavities -> 2 lateral ventricles (1 in each hemisphere), third & fourth ventricle
- filled with cerebrospinal fluid (CSF)
- produce and secrete cerebrospinal fluid to protect and maintain your central nervous system.
cerebrospinal fluid
- acts as a shock receptor
- produced by choroid plexus
- also between tissues of CNS and bones of skull
what are meninges?
- layers of membrane (3 layers)
- protect brain and spinal cord
- made of connective tissue
what are the 3 layers (meninges) that protect the CNS?
- dura mater
- arachnoid
- pia mater
dura mater
- tough outer layer
- skull cap
- prevents direct contact with the skull
arachnoid
- “spider-web” layer
- under the dura
pia mater
- thin inner layer
- close to CNS surface
- in direct contact with tissue of brain
the spinal cord
- tube like structure
- made of grey and white matter
- allows communication between brain & body
- communicated via spinal nerves in PNS
- relays information to & from skin, joints, muscles
- reflexes = brain not always involved
- surrounded by large bones to protect from trauma
how many spinal cord segments are there?
31
what are the spinal cord segments?
-cervical = 8 (C1-C8)
-thoracic = 12 (T1-T12)
-lumbar = 5 (L1-L5)
-sacral = 5 (S1-S5)
-coccygael = 1 (Co)
is the dorsal horn of the spinal cord sensory or motor?
sensory -> sensory nerves (& info) enter this part of the spinal cord
is the ventral horn of the spinal cord sensory or motor?
motor
dorsal columns / funiculus
ascending sensory (nerve) axons
ventral funiculus / columns
descending axons
lateral funiculus
ascending & descending axons
what are neurons?
cells specialised to receive, process and transmit infor via electrochemical signalling
neurites
axons and dendrites -> any projection from cell body of neuron
classification of neurons
- number of neurites
- dendritic tree structure (pyramidal/stellate, spiny/aspinous
- axon length (projection or local circuit neurons)
- neurotransmitter (each have diff function)
- connections (sensory, inter or motor neurons
afferent nerves
- sensory nerves
- signal to CNS (brain) from PNS / sensory surfaces
- enter CNS via dorsal root
efferent nerves
- motor nerves
- info from brain to PNS for action
- exit CNS via ventral root
projection neurons features
- long axons
e.g. pyramidal cells of cerebral cortex, golgi type 1
local circuit neurons features
- short axons
e.g. stellate cells of cerebral cortex, golgi type 2, interneurons
interneurons
form connections between neurons
what are spinal nerves a part of?
PNS
what is potential difference?
- the difference in potential between two points
- potential of charge to move across the membrane
how can you measure potential difference?
- by placing an electrode inside the cell and measuring it vs the electrode outside the cell
- potential always: inside vs outside
what is the resting potential?
- potential difference across a membrane when the cell is non-excited
- no potential difference when the charge is evenly distributed
what do ion channels do?
- permit or prevent movement across a membrane
- selective for particular ions (Na+, K+…)
- a membrane spanning protein complex
- can be gated or non-gated
how does the membrane potential change?
- channel opens until charges reach an equilibrium
- happens freely if not gated and triggered by a stimuli if gated
which channels are open at rest?
- potassium channels
- K+ free to move and equibrilate
which channels are closed at rest?
-sodium channels
why do K+ ions keep flowing out?
-there is more K+ inside than outside
-not only a concentration gradient!!
-> the overall negative charge of the cell pulls K+ back in aswell
= electrical and concentration gradient
when does the equilibrium potential occur?
-where you have no net movement
what is the average resting membrane potential?
around -70mV
-> closer to K+ equibilibrium potential (-90mV) (Na+: +60mV)
what affects the rate of conduction of an action potential?
- myelin
- temperature
- nerve diameter
what is saltatory conduction?
- impulse conduction that jumps from one axon to the next (node to node)
- skips over the myelinated parts of the axon -> faster
2 types of synapses
- electrical
- chemical
electrical synapse
- signals passed directly between connected axons via gap junctions
chemical synapse
- communicate via chemical messengers (neurotransmitters) across junction between axon of presynaptic and cell body of postsynaptic neuron
what does the somatic nervous system do?
controls voluntary movement
what does the autonomic nervous system do?
controls involuntary responses
what are the 4 largest lobes of the cerebral cortex
- frontal lobe
- parietal lobe
- temporal lobe
- occipital lobe
prefrontal cortex
- problem solving
- complex planning
- executive function
- personality
- higher cognitive functions
motor cortex
- planning, control & execution of voluntary movement
- premotor cortex
- supplementary motor area
- primary motor cortex (precentral gyrus, M1)
broca´s area
- production of speech
- usually in left hemisphere (if right handed) -> only in 1 hemisphere of the brain
- broca´s aphasia = disturbance in speech
parietal lobe functions
processing of sensory information
- primary somatosensory cortex (S1)
-> tactile sensation
-> sensory homunculus - posterior parietal cortex
-> integration of sensory informtion
-> spacial perception & attention
-> cognitive functions
what does the sensory homunculus show?
how much of the primary somatosensory cortex is devoted to tactile sensation in certain parts of the body
occipital lobe functions
visual processing center of the brain
- primary visual cortex (V1)
-> straited appearance due to myelinated axons
-> located around calcarine sulcus
-> receives info from the thalamus
-> organised into 6 layers
-> processes info related to all parts - V2, V3, V4, V5: other areas of visual cortex
-> relay different information depending on shape, size and position of objects
temporal lobe
processes sensory information
(+ long term memory formation & visual perception and recognition)
- auditory cortex
-> hearing
-> speech & words
-> pitch & tone - wernicke´s area
-> langauge comprehension
-> aphasia: can procude speech just not understand it
-> left hemiphere
the peripheral nervous system
- formed by sensory (afferent) and motor (efferent) nerve fibres
- these fibres emerge from the brain and spinal cord to innervate every structure in the body
cranial nerves
- 12 pairs of nerves (in back of brain)
- provide motor output and sensory info between brain, face, neck and torso
- ROMAN NUMERALS when naming
spinal nerves
- 31 pairs (one pair per spinal cord segment)
- motor and sensory nerve fibres mixed
sensory (afferent) axons end in_____
sensory receptors
motor (efferent) axons end in______
effectors (muscles)
what are dermatomes?
areas of skin supplied by a single spinal nerve
C1: only spinal nerve without a dermatome
shingles
virus attacks a single spinal nerve -> problems in lesion in dermatome supplied by that nerve
what is a reflex?
- a rapid, involuntary movement in response to a stimulus
- subconcious -> brain gets the info but the brain is not needed for the reflex to occur
function of a reflex?
- protection from harmful stimuli
examples of reflexes
- sneezing
- coughing
- vomiting
- balance and posture
- homeostasis
what is a reflex arc?
- simple circuit in the nervous system
- start: sensory receptors (info relayed by sensory nerves)
- end: effectors (motor nerves)
- do not reach consciousness
monosynaptic
1 sensory and 1 motor neuron
polysynaptic
more than 2 neurons (interneuron(s) needed)
knee jerk reflex - tendon jerk
- stretch reflex (stretch of muscle: hammer tap to patellar tendon)
- stretch of muscle spindle in quadriceps muscle
- sensory fibred to spinal cord synapse with alpha motorneuron
- motorneuron stimulates contraction of the quadriceps muscle (effector)
tendon jerk reflexes
- can be evoked from many muscles
- sensory receptor detects muscle stretch which leads to muscle contraction as efferent motorneuron output to skeltal muscle (somatic motor)
- involves somatic sensory and somatic motor divisions of the PNS
- monosynaptic
flexion (withdrawal) reflex
- polysynaptic
- interneurons needed
control reflexes
- closed loop
- role in control of physiological variables
- stimulus feedback causes response which acts on the stimulus
- muscle stretch -> muscle contraction
- example: tendon jerk reflex
protective reflexes
- open loop -> sensorimotor loop not completed by sensory feedback
- protection from potentially harmful stimuli
- stimulus feedback has no effect on the stimulus
- pin prick e.g. leads to withdrawal from the pin / external stimuli
- example: flexion withdrawal reflex
what is the autonomic nervous system?
- involuntary control of the body´s internal environment
- autonomic reflexes differ from somatic reflexes (efferent output)
- visceral efferent nerves to smooth & cardiac muscle and glands
- two neuron chain: synapse in a ganglion
pre and post ganglionic fibres
what is the somatic nervous system?
conscious voluntary control
crossed extensor reflex
- stimulus causes flexion of leg (withdrawal)
- other leg must extend to support weight of the body to prevent falling over
- sensory info crosses spinal cord via interneurons
what is the enteric nervous system?
- collection of neurons
- form a network = plexuses
- plexuses surround the GI tract
- “second brain”
- located in walls of GI tract as 2 plexi
- can act autonomously to control peristalsis and secretion
- has its own pacemaker cells
- influenced by sympathetic and parasympathetic input hormones and sensory input
what can the ANS be split into?
- sympthetic
- parasympathetic
sympathetic NS
- activated in times of stress, fear and anxiety
- helps body respond when needed
- “fight or flight”
parasympathetic NS
- activated when sedentary
- “rest and digest”
are the sympathetic and parasympathetic NS efferent or afferent pathways?
- efferent
- they control targets via bisynaptic pathway (2 neurons& 2 synapses)
autonomic pathway
2 neurons that synapse in a ganglion
sympathetic neuron
- shorter preganglionic neuron (myelinated)
- longer postganglionic neuron (unmyelinated)
- position of ganglion closer to CNS
parasympathetic neuron
- longer preganglionic neuron (myelinated)
- shorter postganglionic neuron (unmyelinated)
- position of ganglion clsoer to target organ
where do parasympathetic preganglionic neurons originate from?
- cranial nerves (III, VII, IX, X)
- spinal cord levels S2-S4
- craniosacral outflow
- either end of the CNS
where do sympathetic preganglionic neurons originate from?
- spinal cord levels T1-L2
- the lateral horn
- thoracolumbar outflow (thoracic and lumbar spinal cord)
what is the lateral horn?
a small lateral projection of grey matter located between the dorsal horn and ventral horn and contain the neuronal cell bodies of the sympathetic nervous system.
what controls the enteric NS?
- smypathetic & parasympathetic innervention
- hormonal and sensory inputs
location of the ganglia in the parasympathetic NS
- cranial nerves II, VII, IX synapse in ganglia in the head
- cranial nerve X & sacral neurons synapse in ganglia close to target organ
- synapse in the wall of the target organs
location of ganglia in the sympathetic NS
- sympathetic chain
- prevertebral (pre-aortic) ganglia
- helps distribute sympathetic outflow to the whole body
why is signal conduction faster in the parasympathetic pathway compared to the sympathetic?
- the pre-ganglionic neurons in the parasympathetic pathway are longer and myelinated.
parasympathetic distribution of the ganglia
- long preganglionic neurons
- short postganglionic neurons
- only has visceral (organ) distribution
sympathetic ganglia distribution
- series of ganglia that extend from the cranial base to coccyx
- also called sympathetic trunks / paravertebral ganglia
- help distribute neurons throughout the whole body
which neurotransmitter do most post-ganglionic sympathetic neurons release?
noradrenaline onto visceral targets
EXCEPT: sweat glands -> Acht
which neurotransmitter do all post-ganglionic paraysmpathetic neurons release?
Acht at muscarinic receptors on visceral targets
what is the adrenal medulla?
- inner part of the adrenal gland (small organ ontop of each kidney)
- makes chemicals such as adrenaline and noradrenaline which are involved in sending nerve signals
- a modified ganglion
- composed of specialised neuroendocrine cells that secrete noradrenaline and adrenaline directly into the blood stream
- preganglionic sympathetic neurons synapse directly onto cells in the adrenal medulla
fight of flight response
- adrenal secretions act on adrenergic receptors directly & globally
- this activated organs supplied by postganglionic sympathetic neurons (blood vessels, liver, bronchi…)
- also acts on adrenergic receptors of other organs (skeletal muscle…)+
- effects of adrenal medulla secreations lasts longer than direct synapses because the blood stream does not contain enzymes to break down adrenaline and noradrenaline
