Somatic and Automic nervous Systems Flashcards
CNS is made up of the ?
Brain and spinal cord
PNS is made up of?
nerve fibers and cell bodies outside the CNS that conduct impulses to or away from the CNS
Function of the Somatic Nervous system
voluntary nervous system….ability to walk and talk
carries sensation from skin and joints …temperatue
supplies innervation to skeletal muscle
ANS
involuntary/visceral nervous system sympathetic/parasympathetic
Innervates smooth muscle (wall of blood vessels), glands (sweat glands), and viscera (internal
Cell body
Dendrites carry impulses to cell body
Axons carry impulses away from cell body
Has the Soma.
Myelin sheath
Some have layers of lipid and protein around the axon (myelin sheath) that increase velocity and impulse conduction
How does the neurons communicate with each other
Communicate with each other at synapses via release of neurotransmitters
Can excite or inhibit another neuron in order to continue or terminate an impulse
Bipolar Neurons
special” sensory: found in olfactory epithelium, retina, and inner ear
interneurons of spinal cord
one dendrite and one axon
Unipolar (pseudounipolar) Neurons:
General” sensory neurons of the peripheral nervous system
and found in spinal and cranial nerve ganglia
Multipolar Neurons
most common in CNS
motor cells in anterior and lateral horns of spinal cord and autonomic ganglion cells;….motor neurons
multiple dendrites and only one axon
Neuroglia (glial cells)
and function
More abundant than neurons
Nonneuronal, nonexcitable scaffolding of nervous tissue
Support, insulate, and nourish neurons
Types of Neuroglia CNS
Ependymal Cells
Oligodendrocytes
Astrocytes
Microglia
Types of Neuroglia PNS
Satelite cells
Schwann cells
Structure of the PNS
Consists of nerve fibers/axons and nerve cell bodies that connect CNS with peripheral structures
Axons are either myelinated (by Schwann cells) or unmyelinated (these Schwann cells do not produce myelin)
Collection of nerve bodies outside of the CNS is a GANGLION
Ganglion can be motor or sensory
Dorsal root gang is sensory
Peripheral nerves are either cranial (12 pairs) or spinal nerves (31 pairs)
In the CNS what is the Grey matter
Collection of nerve cell bodies called a NUCLEUS
In the CNS what is A TRact
Bundle of nerve fibers/axons connecting neighboring or distant nuclei is called
IN the CNS what is the Whit matter
(remember myelin sheath contain tracts or axons
grey matter and white matter relative to each other in the Spinal cord
gray matter internal H (butterfly) with dorsal/posterior and ventral/anterior gray horns, surrounded by white matter
grey matter and white matter relative to each other in the brain
gray matter surrounds white matter
Somatic Nervous system components and Function
Voluntary nervous system
Composed somatic parts of the CNS and PNS
Provides general sensory and motor innervation to all parts of the body
EXCEPT: viscera in the body cavities, smooth muscle and glands
General somatic sensory/afferent fibers transmit sensations of touch, pain, temperature, and position from sensory receptors
General somatic motor/efferent fibers stimulate skeletal (voluntary) muscle exclusively
Gray matter of the spinal cord is divided into 10 Lamina Namely
I-VI, dorsal gray matter= somatic sensory fibers
Remember dorsal root of spinal nerve carries afferent sensory signals.
VII-IX, ventral gray matter= somatic motor fibers
Remember ventral root of spinal nerve carries efferent motor signals
Laminae X surrounds central canal and contains neuroglial cells and does not play a significant role in relay of information
Tracts of the spinal cord are divided into?
White matter contains axons of ascending and descending tracts
Ascending tracts contain sensory information
Descending tracts contain motor information
Divided into dorsal, lateral and ventral columns
Tracts of the spinal cord
Sensory/Afferent
Motor/Efferent
Sensory/Afferent
Tracts of the spinal cord
Dorsal column: Gracilis and Cuneatus
Fine touch and proprioception,vibration
Lateral spinothalamic tract
Pain (nocioceptive) and temperature
Ventral spinothalamic tract
Crude touch and pressure
Tract Lissauer
Part of spinothalamic tract
Together the ventral spinothalamic tract and lateral spinothalamic tracts are called the Anterolateral Spinothalamic tract
Motor/Efferent
Tracts of the spinal cord
Lateral corticospinal tract
Limb motor
Ventral corticospinal tract
Posture motor
Corticospinal tract
Cortex to spine(Motor)
Spinothalmic tract
Spine to Thalamus
Sensory pathway consist of 3 neurones
1st order neuron links peripheral nerve to spinal cord or brainstem
2nd order neuron links spinal cord or brainstem to subcortical structure in brain
3rd order neuron links subcortical structure to cerebral cortex of brain
Each motor pathway consist of 2 neurones
Cerebral cortex to the ventral horn of the spinal cord
Ventral horn of the spinal cord to the neuro muscular junction
Explain The sensory pathway
dorsal column-medial lemniscal system
Transmits fine touch, proprioception, vibration, pressure
High level of localization, discrimination
Large, myelinated, very fast conducting fibers
1st order neuron: enters spinal cord via dorsal root ganglion; relays sensory from dorsal column to medulla. Ascends spinal cord on ipsilateral side. Synapses at medulla
2nd order neuron: crosses to contralateral side medulla then ascends to thalamus via medial lemniscus. Synapses in thalamus
3rd order neuron: continues to somatosensory cortex; postcentral gyrus in parietal lobe of the brain
Sensory pathway:anterolateral spinothalamic tract
Transmits pain and temperature (lateral portion); crude touch and pressure (ventral portion)
Smaller myelinated, slower conducting fibers
Not able to localize as well, poor discrimination
1st order: enters spinal cord via dorsal root ganglion. May then ascend or descend 1-3 levels on ipsilateral side via Lissauer tract before synapse with 2nd order neurons in dorsal laminae I, IV, V, VI. Pain neurons synapse in substantia gelatinosa- laminae II and III.
2nd order: crosses to contralateral side spinal cord, ascends toward brain via either anterior or lateral spinothalamic tracts. Synapses in thalamus
3rd order: thalamus to somatosensory cortex, postcentral gyrus or parietal lobe
What is the primary somatosensory cortex
Post central gyrus
Somatosensory homunculus
PLS Explain
Slide 15,lecture 2
Sensory input of areas of the body that are far from the core are located more midline in the somatosensory cortex
Sensory input of the areas of the body closer to the core are located more lateral in the somatosensory cortex
Motor pathways:corticospinal tract
Also known as pyramidal tract (pyramids are formed by corticospinal neurons as they run through the medulla)
All other motor pathways outside of the corticospinal tract are called extrapyramidal tracts (think about the extrapyramidal movements seen in ALS or cerebral palsy)
Motor neurons exit precentral gyrus of frontal lobe and travel through the pyramids of the medulla
Lateral corticospinal tract: cross over to contralateral side in medulla then descend the spinal cord via lateral corticospinal tract. Fibers innervate the limbs
Ventral corticospinal tract: remain on ipsilateral side as descend ventral corticospinal tract. Most cross over to contralateral side in spinal cord in the cervical/upper thoracic area. Fibers innervate the axial muscles
Motor Pathway:
Corticospinal tract
Upper motor neuron:
Cerebral cortex to the ventral horn of the spinal cord
Injury above the level of medulla (where decussation occurs) results in paralysis on the opposite side of the body
Injury below level of decussation results in paralysis on same side of body
There are a subset of neurons in this tract that inhibit lower motor neurons- prevents lower motor neurons from firing too frequently. With injury to the upper motor neurons, these inhibitory neurons do not work which results in spastic paralysis and positive Babinski sign
Lower Motor neuron:
Ventral horn to neuromuscular junction
Injury results in paralysis on same side of body
Flaccid paralysis and negative Babinski sign because inhibitory neurons are intact
Motor Homunculus
Precentral gyrus is the primary motor cortex
Motor input to areas of the body that are far from the core are located more midline in the motor cortex
Motor input to areas of the body closer to the core are located more lateral in the motor cortex
ANS component
Visceral efferent (motor) fibers that stimulate smooth (involuntary) muscle in the walls of blood vessels and organs, conducting system of the heart and glands
Sympathetic (thoracolumbar) division
Parasympathetic (craniosacral) division
Visceral afferent (sensory) fibers that conduct pain impulses from internal organs and help to regulate visceral functions.
Components Of Visceral Efferent
Sympathetic and Parasympathetic divisions
Contain a two neuron system
Cell body of the PRESYNAPTIC (PREGANGLIONIC) NEURON is located in the gray matter of the CNS
It’s axon synapses with the cell body of the POSTSYNAPTIC (POSTGANGLIONIC) NEURON
Cell bodies of the second neuron reside in autonomic ganglia outside the CNS and the postsynaptic axons terminate on the effector organ (smooth muscle, conducting system of the heart, glands)
Anatomical difference between the sympathetic and parasympathetic motor divisions of the ANS based on
Location of presynaptic cell bodies
Which nerves conduct the presynaptic fibers from the CNS
Sympathetic visceral motor innervation
Cell bodies of presynaptic neurons located in the INTERMEDIOLATERAL CELL COLUMNS in the gray matter of the spinal cord
Extends between 1st thoracic and 2nd-3rd lumbar segments of the spinal cord
Short presynaptic axons
Cell bodies of the postsynaptic neurons are located either in the paravertebral or prevertebral ganglia
Paravertebral ganglia are linked to form right and left sympathetic trunks/chain on each side of the vertebral column to extend entire length
Prevertebral ganglia are in the plexuses that surround the main branches of the abdominal aorta
Long postsynaptic axons
Sympathetic stimulation results in wide range of responses- not well localized
Function of Sympathetic Visceral Motor Innervation
Fight or Flight”
Skin: vasoconstriction, increases sweat gland activity, hair stands on end, effects are very quick
Head: inhibits lacrimal, nasal and salivary glands (dry mouth), stimulates eye muscles to dilate iris
Thoracic organs: increases heart rate, dilates blood vessels that supply heart, dilate respiratory air tracts, inhibits muscles and glands of esophagus
Gut: inhibits activity of the muscles and glands in viscera
Pelvis: inhibits urination, defecation, promotes ejaculation
Adrenal medulla: secrete great quantities of excitatory hormones into the blood (Epinephrine and Norepinephrine)
Parasympathetic visceral Motor Innervation Location of cellbodies
Cell bodies are located in two areas within the CNS: cranial gray matter of the brainstem and sacral gray matter of the spinal cord= “craniosacral” division
Cranial parasympathetic outflow: cell bodies in the gray matter of the brainstem, fibers exit the CNS within cranial nerves III, VII, IX, and X
Provides parasympathetic innervation to head
Vagus nerve (CNX) provides main innervation to thoracic and abdominal viscera to left colonic flexure
Sacral parasympathetic outflow: cell bodies in the gray matter of the sacral segments of the spinal cord, S2-S4, exit via anterior roots
Provides parasympathetic innervation to pelvic viscera, sigmoid colon and rectum
Parasympathetic pre and post axon structure
Long pre/Short post
Effects of parasympathetic stimulation are more specific and more localised than the effect of sympathetic,true or false.
T
Parasympathetic visceral motor innervation examples
Gastric and intestine: smooth muscle contraction for peristalsis, increased secretions for digestion, allows for defecation and urination, vomiting and swallowing reflexes
Eyes: constriction of pupils
Respiratory: coughing reflex
Cardiac: decreases in heart rate and force of contraction
Function of Visceral Afferent
Sensory fibers that conduct pain impulses from internal organs and help to regulate visceral functions
Responsible for autonomic reflexes
Changes in blood pressure through vascular resistance, heart and respiratory rates
Monitor stretch, temperature, chemical changes and irritation
Interpreted as hunger, fullness, pain, nausea, or well-being
Referred pain- visceral pain identified/perceived as originating from skin or outer body
Pathways travel centrally along sympathetic fibers
