The Nervous System Flashcards
What are the divisions of the nervous system?
CNS and the PNS CNS: brain and spinal cord PNS: sensory and motor nerves Motor nerves: SNS and ANS SNS and ANS both divide into afferent and efferent pathhways
Role of CNS and PNS
CNS: receives and interprets all stimuli and relays nerve impulses to muscle and glands
PNS: enables brain and spinal cord to communicate with the whole body
comprises of 12 cranial nerves and 31 pairs of spinal nerves
Divided into afferent and efferent pathways
afferent (sensory): sending impulses to the brain
efferent (motor): sending impulses to the rest of the body
Motor: divided into somatic (voluntary) and autonomic (unconscious)
Action potential
The action potential is a momentary reversal of membrane potential that is the basis for signaling within neurons.
inner part of axon negatively charged (-70 mv)
if the threshold is reached (-55 mv) action potential is triggered and the axon is depolarised
the action potential causes the axon to become momentarily positively charged
as sodium + and potassium + are pumped into of axon
eventually the axon reaches peak depolarisation at which point sodium channels close and potassium channels open (repolarisation)
Synapses
types
electrical - current spreads between one cell and another - between cardiac cells, smooth cells in intestinal tract
chemical - most common - occurs at the junction between two neurons and at neuromuscular junctions
The cortical lobes:
frontal lobe
parietal lobe
frontal lobe: located in the front of the brain, associated with reasoning, motor skills, cognitive development, and expressive language (Broca’s area)
Parietal lobe: located in the middle of the brain, associated with the processing of sensory information
temporal lobe
occipital lobe
cerebellum
temporal lobe: located at the bottom of the brain, associated with memory, speech perception and language (Wernicke’s area)
occipital lobe: located at the back of the brain, associated with interpreting visual stimuli
cerebellum: responsible for planning of movement
brain stem parts
midbrain - nerve pathway for cerebral hemispheres, auditory and visual reflex centres
pons - receives nerve messages from spine and brain, contains centres for regulation of breathing
medulla - attaches to the spinal cord, controls parts of the body under involuntary control e.g., heart rate
Thalamus
intermediate relay point and processing centre for all sensory impulses (except smell) going to the cerebral hemispheres
integrates neural information from basal ganglia and cerebellum and conveys it to the motor cortex
projections from the thalamus to the central cortex mediate the sleep-wake cycle
hypothalamus
highest integrating centre for ANS - regulates many physiological and endocrine activities through its relationship with the pituitary gland
involved with regulation of body temperature, water balance, sleep-wake patterns, food intake, and behaviour responses associated with emotion, endocrine control and sexual responses
Spinal cord and nerves
Cross-section of the spinal cord consists of an H-shaped core of grey matter
posterior arms of the H are the dorsal horns (where the majority of the sensory axons synapse)
anterior arms are the ventral horns (where the majority of the motor axons synapse
the centre of the H forms the central commissure where connections pass from one side of the spinal cord to the other
the lateral horns (from which ANS fibres are found) are at the ends of the crosspiece of H
ventral medial fissure divides the anterior white matter lying between the ventral horns into two halves
hindbrain
consists of the medulla oblongata, pons, and cerebellum
two prominent vertical ridges (the pyramids) lie on the ventral surface of the medulla oblongata
these demarcate the routes of major motor pathways from the brain to the spinal cord
midbrain (mesencephalon)
small upward continuation of the brainstem connecting the pons to the forebrain
pierced longitudinally by the cerebral aqueduct which connects the third and fourth ventricle
Forebrain
two cerebral hemispheres forming the telencephalon on either side of a region of grey matter immediately above the brain stem known as the diencephalon
important sulci and gyri
― Cingulate gyri – lie immediately above the corpus callosum on the medial aspect of each hemisphere
― Precentral and postcentral gyri lie anterior and posterior to the central sulcus
― Triangular gyrus (frontal operculum) which forms part of Broca’s area
― On the superior surface of each temporal lobe three prominent gyri – the transverse temporal gyri – run transversely to the lateral fissure
― These are the location of the primary auditory cortex
― The posterior side of the lateral fissure divides into two short sulci and the intervening triangular gyrus is the angular gyrus
― Supramarginal gyrus runs superior to the lateral fissure between the inferior postcentral gyrus and the angular gyrus
― Striate cortex – caudate and lentiform nuclei and the intervening white matter
imaging of the brain
― Computer-assisted tomography (CAT) – a narrow beam of x-rays used to examine a slice of tissue
― Can correlated location of brain lesions and different types of aphasia
― Magnetic resonance imaging (MRI) – enables us to study some metabolic processes that CAT cannot
― Functional magnetic resonance imaging (fMRI) – used to monitor local blood flow and detect brain areas involved functions
― Positron emission tomography (PET) – study the function of different areas of the brain by looking at brain glucose and oxygen utilisation can be measured indicating which parts of the brain are involved in specific tasks/functions
― Transcranial magnetic stimulation (TMS) – used to determine the effect of stimulating nerve activity in superficial brain areas by application of a magnetic field through a probe placed on the skin overlying the brain region of interest will stimulate nerve activity and response can be monitored by observing muscular activity
― This technique has increased our understanding of some aspects of swallowing and dysphagia
