Intro to the Nervous System Flashcards
What is the nervous system?
A network of nerve cells and fibres that transmit nerve impulses
Which system does the nervous system work closely with?
The endocrine system
What are the features of the cell body?
They’re the control centre. They have a nucleus and organelles but lack centurions which are required for cell division
What are the features of dendrites?
They’re small projections from the cell body that have branches for increased surface area. They bring afferent processes (sensory).
The mixture between axons and dendrites are referred to as fibres.
What are the features of axons?
Only 1 axon from each cell body carrying impulses away from the cell body and thus are for efferent processes. Surrounded by myelin.
What are the regions between myelin called?
Nodes of Ranvier
In the CNS what is myelin created by?
Oligodendrocytes
In the PNS what is myelin created by?
Schwann Cells
Cells can regenerate in which nervous system, peripheral or central?
Peripheral
What is Neurilemma?
The tight covering around myelin in Schwann cells that play an important role in regeneration (as the PNS can regenerate whereas CNS cannot)
What is neuroglia?
They’re not nerve cells as they don’t conduct nerve impulses but they support, nourish and protect neurons and can divide.
What are the features of sensory neurons?
Have long dendrites and short axons
What are the features of efferent/motor neurons?
They have short dendrites and long axons
What are interneurons?
They’re only in the CNS and form the connecting link between afferent and efferent neurons. They’re short dendrites that vary in axon length.
What is a nucleus?
A cluster of cell bodies in the CNS
What is a ganglion?
A cluster of cell bodies in the PNS
What is a tract?
A bundle of axons in the CNS
What is a nerve?
A bundle of axons in the PNS
What cavity is the CNS encased in?
The dorsal body cavity
Where is the brain?
In the cranial vault
Where is the spinal cord?
Vertebral canal of the vertebral column
What are the brain and spinal cord continuous with?
Medulla oblongata
What are the features of the dura mater?
Dura = outermost layer of the meninges
Tough, white connective tissue that continues with the optic nerve to the back of the eye
What are the features of the Arachnoid mater?
Arachnoid = middle layer of the meninges
Cobweb appearance, a thin layer connecting to the innermost layer
What are the features of the subarachnoid space?
This is the space under the arachnoid that’s filled with cerebrospinal fluid and blood vessels
What are the features of the Pia mater?
Pia = innermost layer of the meninges
Thin and delicate membrane that’s tightly bound to the brain surface and spinal cord
Where does the spinal cord extend from?
The foramen magnum to the first lumbar vertebra
How many segments and spinal nerve are there?
31 segments with a pair of spinal nerves each
The ventral or dorsal routes are in the spinal cord. Which are afferent and which are efferent?
Dorsal = Afferent
Ventral = Efferent
Where does the distal end of the spinal cord extend?
Beyond the conus medullaris that forms the cauda equina
What is the brain divided into?
Cerebrum, diencephalons, brain stem and cerebellum
What is the frontal lobe responsible for?
Voluntary moves, planning and reasoning
What is the temporal lobe responsible for?
Hearing, language, face recognition and memory
What is the parietal lobe responsible for?
Somatosensation and body orientation
What is the occipital lobe responsible for?
V1
What does the central sulcus do?
Separates V5 anteriorly from the somatosensory area behind it
What is the cerebrum?
The largest lobe with a deep longitudinal fissure that splits it into 2 hemispheres that are connected by white fibres called the corpus callosum for communication.
What the outer grey matter known as?
The cerebral cortex
What does the diencephalon consist of?
Thalamus, hypothalamus & epithalamus
Thalamus - 80% of the diencephalon; serve as relay stations for sensory impulses to the cerebral cortex
Hypothalamus - Has a key role in maintaining homeostatis as it regulates visceral activities
Epithalamus - Most dorsal portion and acts like a biological clock
Where is the brain stem?
Between the diencephalons and spinal cord
What are the features of the pons?
Primarily has nerve fibres forming conduction tracts between higher brain centres & spinal cord
What are the features of the medulla?
Continuous with the spinal cord at the foramen magnum. They’re all afferent and efferent connecting brain and spinal cord passes through the medulla.
What is the cerebellum for?
Co-ordination and balance; 2nd largest portion of the brain resting inferiorly to the occipital lobes.
Contain 3 paired bundles of myelinated nerve fibres called cerebellar penduncles that provide a communication pathway between cerebellum and other parts of the CNS.
How do you test that the cerebellum is working properly?
Through the Romberg test where you stand with your feet together and eyes closed to see if able to maintain balance.
How are the spinal cord nerves divided into?
31 paired;
8 Cervical
12 Thoracic
5 Lumbar
5 Sacral
1 Coccygeal
How are the spinal nerves connected to the spinal cord?
Via the dorsal and ventral root (ventral roots come through the anterior horn cell bodies in the CNS)
When do the ventral and dorsal roots of the spine join to form the spinal nerve?
At the vertebral column and exit at the intervertebral formina.
The PNS is split into afferent and efferent nerves. What are the efferent nerves then split into?
The somatic (voluntary - supplies motor impulses to skeletal muscles) and autonomic (involuntary - motor impulses to cardiac, smooth and glandular tissues; parasympathetic and sympathetic)
What are plexi in the somatic nervous system?
Nerve webs formed by spinal nerves reorganising and interweaving. They form 4 plexi.
What are the 4 plexi of the somatic nervous system?
1) Cervical Plexus
Head, neck and shoulders
2) Brachial Plexus
Serve chest, shoulders, arms and hands
3) Lumbar Plexus
Back, abdomen, groin, thighs, knees and calves
4) Sacral Plexus
Pelvis, butt, genitals, thighs, calves and feet
The thoracic nerves don’t feed the plexi but they feed into the chest wall and intercoastal nerves
Why do plexi exist?
Safety measure so that injury at one site/body region may not affect the vital functions of the body
The cervical region of nerves where do they exit?
Above corresponding vertebrae so C1 vertebrae = C1 spinal nerve
The coccygeal region in the spinal originates where?
Below the corresponding vertebrae so C7 and T1 = C8 spinal nerve root
The lumbar region of the spinal cord, where does the spinal cord end and where does the spinal nerve root end?
Spinal cord ends at L1 (conus medullaris) and the spinal nerve roots travel in dural sac below L2 (cauda equina)
Where are electrical impulses from the CNS relayed to?
The neuromuscular junction that converts the signal from electrical to chemical to allow for muscle contraction.
The somatic path of the efferent pathway of the nervous system is split into 2 further areas. What are they?
The somatic peripheral nervous system and the somatic reflex arc
In the somatic peripheral nervous system, where are the sensory and motor neurons?
Sensory - dorsal root ganglia
Motor - brainstem or spinal cord
In the somatic reflex arc, what is a polysynaptic reflex?
Sensory neurons stimulated, activates interneuron that stimulates the motor neuron causing movement (which is one interneuron)
What is the autonomic system of the efferent pathway of the spinal cord split into?
The sympathetic pathway and parasympathetic pathway
Where do the sympathetic fibres of the spinal cord originate?
In the thoracic (cranial nerves_ and the thoraco-lumbar (the 31 pairs of spinal nerves from the spine) at T1-L3/2 at the lateral horn. These feed into the sympathetic chain at either side of the vertebral column that leave as mainly unmyelinated post-ganglionic fibres to the organ destination.
What are the 4 routes of the pre-ganglionic fibres of the sympathetic pathway of the autonomic system of efferent fibres in PNS?
1) Synapse with para-vertebral ganglion and post-ganglion via grey communication branch that rejoins at the spinal nerve
2) Synapse with para-vertebral ganglion but exit sympathetic nerve for thoracic activity
3) Don’t synapse and exit splanchnic nerve
4) Travel via the splanchnic nerve to medulla without synapsing
There are some exceptions being ACh which synapses at pre-gang and Noradrenaline at post-ganglionic synapse
Which thoracic spine nerves involve the sympathetic chain?
T1 and T2
Short pre and long post-ganglionic fibres
Of the sympathetic chain in the autonomic nervous system, how do the thoracic spine nerves travel?
1) Stay at the same level
2) Goes up or down the chain until reaching whichever organ it has to innervate
3) Travels to another ganglion in the bodies periphery that’s closer to the organ it needs to innervate
What is the exception to the rule of parasympathetic and sympathetic NS neurotransmitters?
The adrenal medulla - directly innervated by the pre-ganglionic axon where ACh is at pre-gang but adrenaline and noradrenaline secretion are at the post-gang
& sweat glands where ACh is the neurotransmitter at both pre-and-post synapses
The parasympathetic fibres of the autonomic system of the efferent nerves of the PNS originate from which 4 cranial nerves and sacral fibres?
CN III = eye constriction - Oculomotor
CN VII = salivary glands - Facial
CN IV = salivary glands - Glossopharyngeal
CN X = slows heart rate - Vagus
The sacral nerves supply the bowel and bladder
Long pre and short post-ganglionic neurones. Exclusively use ACh as neurotransmitter.
= Cranio-Sacral
What cells are in the CNS and what do they do?
Astrocytes - structural and metabolic support
Microglia - Macrophage cells - immune support
Oligodendrocytes - Myelinate neurones in CNS
Ependymal Cells - Line ventricles, produce CSF, homeostasis
What cells are in the PNS and what do they do?
Schwann Cells - Myelinate neurones in PNS
Satellite Cells - Structural/metabolic support in PNS ganglia
What nerves does the somatic system deal with?
43 = 31 spinal pairs and 12 cranial nerves
What is the brain divided into?
Cerebrum, Diencephalons, Brain Stem & Cerebellum
What surrounds the spinal cord?
Bone, meninges, cerebrospinal fluid
