Neuro - Part 5 Flashcards
What does the somatic motor system do? What is it composed of?
- supports body against gravity, establishes posture, and allows voluntary movement to occur
- composed of:
- give directions that control the sequential cord activity: cerebral motor cortex, basal nuclei, cerebellum, thalamus, brainstem
- contain circuits for movement: spinal cord, peripheral nerves
What is posture and movement dependent on?
- dependent on a combination of voluntary actions controlled by higher brain centers and involuntary reflexes coordinated by the spinal cord
What must the CNS do to control body movement? What 2 receptors are important for this?
- the CNS must:
- assess the effect of gravity on the muscles
- determine the initial position of body parts to be moved
- detect any discrepancy between the intended movement and movement that naturally occurs
- 2 receptors: muscle spindle + golgi tendon organ
What is a reflex? What is a reflex arc? What are the 5 components of the reflex arc?
- reflex: involuntary , qualitatively unvarying motor response of the nervous system to a stimulus
- reflex arc: neuronal circuit that directs this motor response
- receptor
- sensory neuron
- one or more synapses in the CNS
- motor neuron
- target organ
What ways can reflexes be classified?
- monosynaptic (direct contact between sensory + motor neurons) x polysynaptic (involve interneurons,more common)
- ipsilateral x contralateral
- segmental (refle arc passes through only a small segment of spinal cord and a small rostrocaudal region of the brainstem) x intersegmental (reflex arc passses through many segments of spinal cord and several major brain divisions)
- somatic x autonomic
Describe the stretch reflex or tendon reflex
- a primarily monosynaptic reflex
- afferent axons from a muscle stretch receptor directly synapse w/ spinal cord alpha motor neurons which cause contraction of that are muscle
- stretch receptor for tendon reflex is the muscle spindle
What is the patellar reflex?
- monosynaptic reflex
- excited by tapping the tendon of the quadriceps femoris muscle immediately distal to the patella
- test extensor reflex mediated by femoral nerve
- most reliable test of tendon reflex
- cord segment involved: L4-L6
What does the stretch reflex counteract?
- gravity
What is the inverse stretch reflex?
- the duration and force of muscle contraction associated with the stretch reflex is mitigated to some degree by the golgi tendon organ
- receptor is sensitive to muscle tension increasing their firing rate when the muscle contracts
- excites inhibitory neuron in spinal cord
- inhibits alpha motor neuron causing contraction
- leads to muscle relaxation
- ** prevents excess tension on the muscle
T/F: sensory inputs to a segment of the spinal cord can only influence motor neurons in the same segment
- false
- B
- A
- A
- B
What is the flexor reflex or withdrawal reflex?
- a coordinated postsynaptic reflex in high all the flexor muscles of the limb contract in response to a noxious stimulus
- reciprocal innervation
-the force and duration of the withdrawal reflex are proportional to the intensity of the noxious stimulus applied
What is the clinical application of the withdrawal reflex?
- assess integrity of sensory and motor reflex pathways that mediate flexion of limbs
- elicited by applying pressure to base of the toenail
- thoracic cord segment: C6-T4
- pelvic cord segment: L4-S1
- clinically, a intact reflex, whether normal or exaggerated, tells the clinician that the lesion does not involve that area of the PNS/CNS
- will be present even if the neuroma is cranial or causal to the reflex circuit as been damaged
- exaggeration may occur w/ lesions affecting UMNs cranial to reflex
What are the CNS areas involved with voluntary movement?
- Primary Motor Cortex
- most voluntary movements initiated by the cerebral cortex are achieved when the cortex activates “patterns” of function stored in lower brain areas
- cerebellum
- basal nuclei
- spinal cord
- brainstem
What are the two general forms movement is divided into?
- dominated by flexor muscles
- largely learned, voluntary, conscious and skilled
- fairly discrete contraction of a few muscle groups (many distal to spinal cord)
- dominated by extensor muscles
- postural, antigravity muscle activity, generally subconscious and involuntary
- long term contraction of larger groups of muscles (many located closer to spinal cord)
How are the two forms of movements controlled?
- skilled voluntary movement of distal musculature (flexors) is primarily controlled by a LATERAL SYSTEM (LATERAL FUNICULUS) of LMN and UMN spinal tracts
- posture and anti-gravity activity of the proximal and axial musculature (extensors) is controlled by a more MEDIAL SYSTEM (VENTRAL FUNICULUS) of neurons and tracts
T/F: CNS structures that control movement have a hierarchal organization
- true
- simple movements/movement patterns: more caudal CNS regions
- complex/skilled patterns: progressively more rostral regions
Describe the role of the spinal cord in motor function
-spinal cord is the most caudal and simples level of movement control
- contain the alpha LMN innervating skeletal muscle fibers
- contain interneurons and complex neural circuits for motor control (spinal reflexes)
- execute low-level commands that generate proper forces on individual muscle groups to enable adaptive movements (the # of muscle fibers innervated by a single LMN decreases as the need for fine control of a muscle increases)
How does the motor system maintain posture?
- providing a tonic excitatory bias to motor circuits that excite extensor muscles
- modulating stretch-reflex circuits
T/F: proprioceptive information is vital for movement
- true;
- muscle spindles and golgi tendon organs help to provide this information
- these receptors are also components of some spinal reflexes: important for basic understanding of motor control
What is walking/locomotion dependent on?
- alternation between extension and flexion which is largely generated by spinal cord reflexes
- stretch reflex (muscle spindle): contracts muscle being stretched
- inverse muscle stretch (golgi tendon organ): relaxes muscle being tensioned
- withdrawal reflex/flexor reflex (proprioceptive and nonproprioceptive receptors): cause flexion of stimulated limb
- ** protects body from injury BUT can be MODULATED (overridden) by the cortex!
Describe the crossed extensor reflex and positive supportive reaction
- about .2-.5s after a stimulus elicits a withdrawal reflex in one limb, the opposite begins to extend
- ** crossed-extensor reflex only works when weight bearing
- if laying down, no reflex is NORMAL
- if reflex is present = PATHOLOGIC, UMN lesion expected
What are central pattern generators (CPGs)?
- neuronal networks in the CNS that produce oscillatory outputs used for controlling rhythmical motor activity
- locomotion, scratching, chewing, breathing
- contain excitatory and inhbitory neurons
T/F: activity in the muscles of the trunk, neck, and tail are interlinked
- true
Constant proprioceptive input from all body + limb muscles both activates the reflexes and sends sensory information to the cerebellum for use in coordination of motor activity. This gives to rise to:
- conscious awareness of posture and movement
UMN tracts __________, __________, and __________ muscle activity of limbs and body
- initiate, modify, and terminate
What are the two major descending motor system pathways from brain to spinal cord?
What are the 4 major axon tracts of the brainstem UMN pathways
- medial (ventral column): axons travel in medial regions of the white matter and synapse within medial regions of the grey matter
- vestibulospinal tract
- reticulospinal tract
- tectospinal tract
- lateral (lateral column): axons run in a more lateral region of the white matter and synapse in the lateral spinal grey matter
- rubrospinal tract
What is the major role of the medial UMN pathways?
-to maintain the body subconsciously in an upright position against the pull of gravity
- control of axial + proximal EXTENSOR musculature
- bilateral control
- prevents animal from collapsing
What are features of the 3 medial UMN pathways?
- vestibulospinal tract
- regulates antigravity muscle tone
- receives sensory information form the vestibular system
- reticulospinal tract
- regulates antigravity muscle tone
- initiate and control the speed of to-and-fro rhythmicity of walking
- modulate consciousness, arousal,and attention
- plays important role in pain perception, respiration, and circulatory function
- tectospinal tract
- involved in reflex orientation of the head towards environmental stimuli + rapid reflex movement of eyes
- axons only project as far as the upper cervical regions of the spinal cord (muscles that move the head)
- process visual, auditory, and somatosensory info about the relative position of stimuli in the environment w/ respect to the organism (coordinate dad and eyes to fix gaze on stimuli)
What are features of the lateral UMN pathway?
- controls distal limb musculature associated with movement
- exerts unilateral control over a limited number of muscles in the distal limb (often flexors associated with skilled movements of extremities)
- receives a lot of input from higher levels of the motor system (provides a means for the motor cortices to INDIRECTLY influence the spinal LMNs of distal limb flexor musculature)
- receives significant input from the CEREBELLUM (synchronizes muscle activity by fine tuning movement initiated by corticospinal tract)
What are other brainstem influences in the motor system?
- sensory organs in the face/head
- ex: eye + vestibular apparatus
- simple segmental reflexes can be organized at the brainstem levels without significant control from other levels of the motor system
The ability to control the most dexterous skilled movements derives from:
- synaptic termination pattern of several axons
- axons bypass not only the brainstem motor pathways to the cord but also the premotor neurons of the spinal cord
- a given corticospinal neuron contains smaller #s of alpha neurons
- causes increased independence of the actions of different muscles (ex: moving individual fingers)
How does the cerebellum control posture and movement?
- posture: the cerebellum coordinates overall posture by coordinating contraction-relaxation of all muscles in the body used for maintaining posture, BOTH at rest + during movement
- failure to establish a postural platform prevents normal,coordinated movement
- movement: the cerebellum coordinates initiation of movement, the actual movement itself, and termination of movement
- ** CANNOT initiate movement per se
How does the cerebellum and the executive motor planning areas interact?
- a copy of the planned movement is sent to the cerebellum which then establishes the postural platforms
- the cerebellum feeds back to the motor planning centers informing them that the posture has been established
- the executive centers then direct the pyramidal and extrapyramidal tracts so that movement is initiated
What are the subdivisions of the ANS and some features of each?
- parasympathetic system “rest + digest”
- responsible for processes that conserve and store energy
- day-to-day control of viscera for basic functions (ex: breathing at rest, digestion, elimination)
- anatomically arises from the cranial and sacral-spinal nerves
- craniosacral system
- sympathetic system “fight + flight”
- function under stress: enables vigorous activity with rapid production of energy (ATP)
- increases HR, respiration,change blood flow to activate muscles,dilate pupils for increased vision
- anatomically arises from that columnar cord
- thoracolumbar system
T/F: most viscera receive info from either the SNS or PSNS but not both
- false; despite different origins, most viscera receive both sympathetic and parasympathetic input, with the systems acting together in a antagonistic fashion to maintain homeostasis
- input balance determines organ function
Although the ANS is usually defined as visceral motor system, it has ________, ________, and _________ components
- afferent, central, and efferent components
- target viscera are usually part of reflex pathways + CNS structures like the hypothalamus
What are characteristics of pre-ganglionic and post-ganglionic neurons in the ANS?
- connect the CNS to the target organ
- the somatic motor system has only ONE LMN connecting skeletal muscle and spinal cord
- the ANS pre-ganglionic neuron has its cell body in the CNS and synapses with the post-ganglionic neuron in the peripheral ganglion
In both sympathetic and parasympathetic systems cell bodies of the ___________ neurons are located in the CNS
- preganglionic
In parasympathetic innervation, cranial and sacral pre-ganglionic fibers leave the CNS to synapse in:
- specific ganglia near the target organs
In sympathetic innervation, fibers to the abdominal and pelvic viscera are supplied by:
- thoracic and lumbar splanchnic nerves
The post-ganglionic neuron has its cell body in the peripheral ganglion ______ the CNS. In the parasympathetic system,the ganglion is usually _________ to the target organ
- outside
- very close
Post-ganglionic neurons usually have _______ _______ ______ axons. What are some features?
- slow conducting unmyelinated axons
- innervate SMOOTH MUSCLE (in blood vessels + viscera), CARDIAC MUSCLE (heart), and GLANDULAR TISSUE (visceral + non-visceral glands)
- they can excite or inhibit the target tissue
- no generalization to explain whether SNS or PSNS will cause + or - of a particular organ, must understand organ function
- synaptic boutons are varicosities distributed along the length of the branches
All pre-ganglionic neurons are ___________ in both sympathetic and parasympathetic systems. They secrete _________ in the synapse with the post-ganglionic neuron
- cholinergic
- acetylcholine
Post-ganglionic neurons secrete different neurotransmitters.
- parasympathetic post-ganglionic neurons are __________ and secrete ________
- most sympathetic post-ganglionic neurons are ___________ and secrete ____________
- cholinergic, acetylcholine
- adrenergic, norepinephrine
____________ is synthesized in the axoplasm of the terminal endings and at secretory vesicles
- norepinephrine
- basic steps:
- thyrosine ——hydroxylation—> dopa
- dopa ——decarboxylation——> dopamine
- transport of dopamine into vesicles
- dopamine ——hydroxylation——> norepinephrine
- norepinephrine ——methylation——> epinephrine**
- ** only in ADRENAL GLAND
The enteric nervous system has _______ fibers. What are some features of these fibers?
- NANC: non-adrenergic, non-cholinergic fibers
- extensively innervate the enteric nervous system
- very important in the physiological regulation of the GI tract, genitourinary tract, and selected blood vessels
- ex: NANC fibers produce NITRIC OXIDE
What are features of the enteric nervous system?
- regulation of GI physiology is mediated by the enteric nervous system, which is a intrinsic system in the wall of the GI system
- sensory +motor components
- complex network that inclues the myenteric plexus and sumucosal plexus
- nerve endings in the gut wall + mucosa convey chemical, mechanical, and stretch sensory information
- in the PSNS and SNS innervation appears to modulate the enteric NS in a regulatory manner
- GI has cholinergic, adrenergic, and NANC fibers
What are features of nicotinic receptors?
- bind to ACh
- ligand-gated ion channels found in autonomic ganglia of both SNS and PSNS (Nn)
- also found at neuromuscular junction in skeletal muscle (Nm)
- activation results in EPSP’s of the postsynaptic neuron
What are features of muscarinic receptors?
- bind to ACh
- GPCR’s found on all effector cells that are stimulated by pstganglionic cholinergic neurons of ether the SNS or PSNS
- ACTIVATE SECOND MESSENGERS
- 5 subtypes: M1, M2, M3, M4, M5
- signal through GI or Gq family of G proteins
What are features of adrenergic receptors?
- located at the synapses between peripheral target tissues and synaptic post-ganglionic neurons that release NE
- also stimulated by the release of cathecolamines from adrenal gland
- GCPRs
- 2 divisions: alpha + beta
What are the two divisions of adrenergic receptors and some features?
- alpha receptors
- subtypes: a1 (Gq) and a2 (Gi)
- ex: induce vasoconstriction of most blood vessels; raise blood pressure - beta receptors
- subtypes: B1, B2, B3 (Gs)
- ex: B1 in he heart increases HR and contraction force
- Beta Blockers: decrease HR and present arrhythmias
What are features of dopamine receptors?
- dopamine mediates numerous physiological effects in the CNS and at the peripheral target organs
- released by some post-ganglionic sympathetic neurons synapsing with specific organs like renal vessels
- bind to dopaminergic receptors: GPCR
- activate different cellular responses resulting in a EPSP or IPSP
- subtypes: D1, D2, D3, D4, D5
What are characteristics of the parasympathetic nervous system?
- craniosacral system that conserves and restores the energy sources of the body
- the pre-ganglionic fibers are relatively long,projecting toganglia located in the vicinity of or in the wall of their target tissues
- post-ganglionic neurons have short axons
- does NOT innervate structures of the body wall + extremities
- have greater degree of independent control, as well as more precise control of tissues and organs compared to SNS
What are features of the sympathetic nervous system?
- thoracolumbar system that preps body for emergency situations
- post-ganglionic fibers reach effector organs by accompanying the vasculature supplying them. Widely distributed as blood vessels
- some effector organs are controlled solely by the sympathetic division
- sweat glands, piloerector muscles, most blood vessels
What are actions of the parasympathetic and sympathetic systems?
What part of the adrenal gland is important to tone? What does it produce?
- medulla
- Epinephrine + Norepinephrine
- adrenal gland is essentially a postsynaptic ganglia/neuron of the sympathetic nervous system
- secretes neurotransmitters via chromaffin cells from amino acid tyrosine
What are the results of the fight of fight response
What are features of the baroreceptor reflex?
- ANS
- refelx arc composed by:
- baroreceptor: receptor for blood pressure
- afferent neurons: carry info to medulla oblongata
- brain stem enters (medulla): process info and coordinate a appropriate response
- efferent neurons: direct changes in heart and blood vessels
Describe the pupillary light reflex
- when bright light shines directly into the eye, the pupil constricts (miosis) due to contraction of circumferential arranged smooth muscle of the iris
- requires the retina, optic nerve, 2 central nuclei, the oculomotor nerve, ciliary ganglion, and ciliary nerve
- the pupillary response that occurs in the illuminated eye is the DIRECT RESPONSE
- the pupillary response that occurs in the not illuminated eye is the CONSENSUAL or INDIRECT RESPONSE
When a flashlight is shown into an animals eye, light stimulates photoreceptors in the retina. What happens after?
- sensory potentials are transmitted to the brainstem along the optic nerve (CN II)
- through several interneurons, PARASYMPATHETIC CHOLINERGIC neurons (CN III) stimulate the constructor smooth muscle of the iris
- pupillary diameter becomes smaller (MIOSIS)
Describe Horner’s syndrome
- loss of sympathetic input to the head due to decreases stimulation of the smooth muscle of the eye and periorbita
- clinical signs:
- enophthalmos: affected eye appears sunken
- narrowing of palpebral fissure: secondary to paralysis
- pupillary constriction ansicoria (inequality of pupil size)
- prolapse of 3rd pupil
D?
