Module 3 Flashcards
- neural pathways that control the sequence and pattern of muscle contractions
- distributed throughout brain and spinal cord
Motor System
- consists of a single motor neuron and the muscle fibers that it innervates
- for fine control, a single motor neuron innervates only a few muscle fibers
- EXAMPLE: eye muscle
- for larger movements, a single motor neuron may innervate thousands of muscle fibers
- EXAMPLE: postural muscles
Motor Unit
- is the set of motoneurons innervating fibers within the same muscle
motoneuron pool
- force of muscle contraction is graded by recruitment of additional motor units (graded response)
- as additional motor units are recruited, more motor neurons are involved and more tension is generated
Size Principle of Muscles
Types of Motor Neurons
- Alpha Motor Neurons
2. Gamma Motoneurons
- innervate extrafusal skeletal muscle fibers
- action potentials in α motor neurons lead to action potentials in the extrafusal muscle fibers they innervate, which results in contraction
Alpha Motor Neurons
- innervate specialized intrafusal muscle fibers
- adjust the sensitivity of the muscle spindles(so that they respond appropriately as the extrafusal fibers contract and
shorten)
Gamma Motor neurons
Types of Muscle Fibers
- Extrafusal Fibers
- Intrafusal Fibers
- make up the bulk of muscle
- innervated by alpha motor neurons
- provide the force for muscle contraction
Extrafusal Fibers
- smaller than extrafusal muscle fibers
- are innervated by gamma motor neurons
- encapsulated in sheaths to form muscle spindles
- are too small to generate significant force
Intrafusal Fibers
- central role in skeletal muscle control
- cell bodies are topographically arranged within the ventral horn of the spinal cord
- axons innervate skeletal muscle fibers
- cell bodies receive numerous synaptic connections from:
o proprioceptors
higher levels of the CNS including the brainstem, basal ganglia, cerebellum, and motor cortex
Alpha Motor Neuron
Topographic Arrangement
- muscles of the trunk are medial
- muscles of the extremities are lateral
- limb flexors are dorsal
- limb extensors are ventral
¥ synapse with the pool of motor neurons by which they are stimulated
¥ predominantly inhibitory
¥ bring about recurrent or feedback inhibition
Renshaw Cells
What type of synaptic arrangement is exemplified by Renshaw cells?
one to many
What neurotransmitter is released by Renshaw cells?
Glycine
What type of neuronal circuit is exemplified by Renshaw cells?
Divergent
sense of awareness of:
- position of the body in space
- progress of the movement by sensory receptors within the muscles and joints
Proprioception
- mechanoreceptors within muscles and joints
- provide the CNS with information regarding muscle length, position and tension (force)
Proprioceptors
More than half of all the nerve fibers that ascend and descend in the spinal cord are __.
Propiospinal fibers
two major proprioceptors:
O Muscle Spindle
O Golgi Tendon Organ
- small, encapsulated intrafusal fibers
- lie in parallel with extrafusal muscle fibers
- send information to the nervous system about muscle length or rate of change of length
- innervation is as follows:
1. efferents via gamma motor neurons - regulates sensitivity of the spindles
2. afferents via group Ia (primary or annulospiral endings) and group II fibers (secondary endings) - respond to muscle stretch
Muscle Spindles
True or False
The finer the movement required, the greater the number of muscle spindles in a muscle.
True
Types of Intrafusal Fibers in Muscle Spindles
- Nuclear Bag Fibers
o detect the rate of change in muscle length (fast, dynamic changes)
o innervated by group Ia afferents
o have nuclei collected in a central “bag” region
2. Nuclear Chain Fibers o detect static changes in muscle length o innervated by group II afferents o more numerous than nuclear bag fibers o have nuclei arranged in rows
Role of Muscle Spindles
- comparators for maintenance of muscle length
- important during goal-directed voluntary movements
o voluntary changes in muscle length are initiated by motor areas of the brain
o includes changes to the set-point of the muscle spindle system
- simultaneous activation of extrafusal fibers (by alpha motor neurons) and intrafusal fibers (by gamma motor neurons)
- readjusts the sensitivity of muscle spindles continuously as the muscle shortens
- allows the muscle spindles to be functional at all times during a muscle contraction
Co-activation
- mechanoreceptors that lie within the tendons of muscles immediately beyond their attachments to the muscle fibers
- respond to degree of tension within muscles
- group Ib afferent fibers relay this information to the CNS (in particular the spinal cord and cerebellum)
Golgi Tendon Organ
- rapidly executed, automatic, and stereotyped response to a given stimulus
- simplest form of irritability associated with the nervous system
Reflex
- neurons participating in a reflex form a reflex arc, which includes:
o receptor
o afferent neuron that synapses in the CNS
o efferent neuron that sends impulses to an effector
o interneurons may be present between the afferent and efferent neurons
Reflex arc
Afferent vs Efferent
Remember SAME!
Sensory = Afferent Motor = Efferent
Classification of Neural Reflexes
- Efferent division that controls the effector
- Integrating region within the Nervous system
- Time at which the reflex develops
- The number of neuron in the reflex pathway
Classification of Neural Reflexes: Efferent division that controls the effector
a. Somatic motor neurons - control skeletal muscles
b. Autonomic neurons - control smooth and cardiac muscle, glands, and adipose tissue.
Classification of Neural Reflexes: Integrating region within the Nervous system
a. Spinal reflexes do not require input from the brain
b. Cranial reflexes are integrated within the brain
Classification of Neural Reflexes: Time at which the reflex develops
a. Innate (inborn) reflexes are genetically determined.
b Learned (conditioned) reflexes are acquired through experience
Classification of Neural Reflexes: The number of neuron in the reflex pathway
a. Monosynaptic reflexes have only two neurons: one afferent (sensory) and one efferent. Only somatic motor reflexes can be monosynaptic.
b. Polysynaptic reflexes in crude one or more interneurons between the afferent and efferent neurons. All autonomic reflexes are polysynaptic because they have three neurons: one afferent and two efferent.
- also known as patellar tendon-tap reflex, knee-jerk reflex or myotactic reflex
- stretching of a muscle stimulates the muscle spindle afferents
plays an important role in the control of posture
Muscle Stretch Reflex
Components of a Muscle Stretch Reflex
- Dynamic Stretch Reflex
2. Static Stretch Reflex
- caused by rapid stretch or unstretch
- transmitted from primary sensory or annulospiral endings of the muscle spindles
- oppose sudden changes in muscle length
- lasts within a fraction of a second only
Dynamic Stretch Reflex
- elicited by the continuous static receptor signals
- transmitted by both primary and secondary endings
- causes the degree of muscle contraction to remain reasonably constant
- continues for a prolonged period
Static Stretch Reflex
Damping Function of Stretch Reflexes
- muscle spindles prevent oscillation or jerkiness of body movements
- ensure that contraction is relatively smooth, even though the motor nerve to the muscle is excited at a slow frequency
- reinforcement technique for eliciting deep tendon reflexes
o fingers are locked together and one hand pulls against the other while reflex is evoked - physiologic basis
o when one muscle is stretched, it facilitates a substantial number of alpha motor neurons
o transient increase of gamma motor neuron activity
Jendrassik’s Maneuver
Jendrassik’s maneuver facilitates multiple alpha motor neurons. What does this mean?
easier recruitment
If they are being facilitated, where are they located in the neuronal pool?
facilitated pool (it’s easier to excite)
- oscillation of a stretch reflex
- ordinarily occurs only when the stretch reflex is highly sensitized by facilitatory impulses from the brain
Clonus
- elicited by noxious stimuli
- transmitted by group II, III, IV fibers
- possesses at least one interneuron, and so the most basic flexion reflex is disynaptic
- usually many muscles are involved through polysynaptic pathways
- to achieve withdrawal of a limb:
o flexor muscles in the limb must contract while the extensor muscles relax
Flexor Withdrawal Reflex
What type of neuronal circuit is exemplified by flexor withdrawal reflex?
Divergent
Receptor that senses pain
Nociceptor
- supports the body as the weight shifts away form the painful stimuli
- stimulation of the flexion reflex frequently elicits extension of the contralateral limb about 250 ms later
- long latency between flexion and crossed extension represents the time taken to recruit interneurons
- helps to maintain posture and balance
Crossed extensor reflex
- ensures that the extensor muscles acting on a joint will relax while flexor muscles contract
- neuronal circuit that causes this reciprocal relation is called reciprocal innervation
Reciprocal Inhibition
Components of Flexor Withdrawal Reflex
- diverging circuits to spread the reflex to the necessary muscles for withdrawal
- reciprocal inhibition circuits to inhibit the antagonist muscles
- circuits to cause afterdischarge lasting many fractions of a second after the stimulus is over
What type of neuronal circuit is exemplified by prolonged afterdischarge in crossed extensor reflex?
Reverberating/Recurrent
- Golgi tendon organs monitor muscle tension
- negative feedback mechanism that prevents development of too much tension on muscles
- when tension becomes extreme, reflex inhibitory effects lead to instantaneous relaxation of the entire muscle (lengthening reaction)
Inverse Myotactic Reflex
What are the four major spinal cord reflexes?
- Muscle Stretch Reflex
- Golgi Tendon reflex
- Flexor withdrawal reflex
- Crossed extension reflex
of synapses: Monosynaptic
stimulus: Muscle stretch
afferent fibers: Group Ia fibers
efferent response: Muscle contraction
Muscle Stretch Reflex
of synapses: Di/polysynaptic
stimulus: Muscle tension
afferent fibers: Group Ib fibers
efferent response: Muscle relaxation
Golgi Tendon reflex
of synapses: Polysynaptic
stimulus: Pain
afferent fibers: Group II, III, IV fibers
efferent response: Ipsilateral muscle flexion
Flexor withdrawal reflex
of synapses: Polysynaptic
stimulus: Pain
afferent fibers: Group II, III, IV fibers
efferent response: Contralateral muscle extension
Crossed extension reflex
- caused by transection of the spinal cord
- loss of spinal reflexes (areflexia) and flaccid paralysis below the level of the injury
- over the ensuing weeks, spinal cord activity below the level of the lesion returns as the excitability of undamaged neurons increases
- may give rise to spasticity of the paralyzed muscle groups
Spinal Shock
Events in Spinal Shock
- Neurogenic Shock
- Areflexia
- Incontinence
- arterial blood pressure falls instantly
- demonstrates that sympathetic nervous system activity becomes blocked almost to extinction
Neurogenic Shock
- may last 2 weeks to several months
- order of return: stretch reflexes, flexor reflexes, postural antigravity reflexes, remnants of stepping reflexes
Areflexia
- sacral reflexes for control of bladder and colon evacuation are suppressed
Incontinence
- impairment or loss of motor and sensory function in the arms, trunk, legs, and pelvic organs
Tetraplegia / Quadriplegia
- impairment of function of the legs and pelvic organs
Paraplegia / Biplegia
- total paralysis of the arm, leg, and trunk on the same side of the body
- does not usually result from spinal cord injuries but from strokes
Hemiplegia
- polysynaptic reflex useful in testing for spinal shock
- checks anal sphincter contraction in response to squeezing the glans penis
o absence indicates spinal shock
o first reflex to return after spinal shock - once this reflex has returned, all remaining neurologic deficits are considered permanent
Bulbocavernosus Reflex
- contains motor areas- stimulation will elicit contralateral movements
- displays somatotopic arrangement
- areas of the body that are capable of especially refined and complex movements (i.e. fingers, lips, and tongue) have a disproportionately large area of representation
Cerebral Cortex
- divided into three sub-areas, each of which has its own topographical representation of muscle groups and specific motor functions:
o PRIMARY MOTOR CORTEX
o PREMOTOR AREA
o SUPPLEMENTARY MOTOR AREA
Motor Cortex
- located in precentral gyrus or Brodmann area 4
- responsible for the execution of movement (programmed patterns of motor neurons and voluntary movement)
- is somatotopically organized (motor homunculus)
Primary Motor Cortex
Epileptic events in the primary motor cortex cause __
Jacksonian seizures
- immediately anterior to the lateral portion of the primary motor cortex
- forms a portion of Brodmann area 6
- responsible for generating a plan for movement - transferred to primary motor cortex for execution
- stimulation causes activation of groups of muscles
Premotor Area
- located in the medial portion of Brodmann area 6 just anterior to the lower extremity portion of the precentral gyrus
- stimulation causes activation of bilateral muscle activation (usually upper extremities)
- programs complex motor sequences
- active during mental rehearsal for a movement
Supplementary Motor Area
- motor speech area
- converts simple vocal utterances into whole words and complete sentences
Broca’s Area
- controls conjugate eye movement required to shift gaze from one object to another
Frontal Eye Field (Brodmann Area 8)
- enables movement of head correlated with eyes
Head Rotation Area
- when damaged, hand movements are lost (motor apraxia)
Area For Fine Movements Of Hand
- carried by the corticospinal (pyramidal) and extrapyramidal tracts
- also sends numerous collaterals to the basal ganglia, cerebellum and brainstem
Motor Outflow of Cerebral Cortex
- motor areas receive inputs from many sources
o predominant sensory input is from the somatosensory system, which receives its input from the thalamus - afferent information is also received from the visual system, cerebellum, and basal ganglia
o used to refine movements, particularly to match the force generated in specific muscle groups to an imposed load
Motor Input of Cerebral Cortex
What are the three sub-areas of the motor cortex?
Primary Motor Area- execution of movement
Premotor Area - planning of movement
Supplementary Motor Area - bilateral muscle movement
- originates over a wide area of cortex including both motor and somatosensory areas
- more than 80 per cent of the fibers decussate at the pyramids (cervicomedullary junction)
- predominant pathway for the control of fine skilled manipulative movements of the extremities
- loss of precise hand movements is a hallmark feature of lesions to the corticospinal tract
Corticospinal Tract
CORTICOSPINAL TRACT
- Motor Cortex
- Corona radiata
- Internal capsule
- Cerebral peduncle
- Brainstem
- Cervicomedullary junction*
- Corticospinal tract (A/L)
- Anterior horn cell
- Ventral root
- Peripheral nerve
- Neuromuscular junction
- Muscle
- conveys nerve impulses from the motor cortex to skeletal muscles of the head and neck
- axons of UMNs descend from the cortex into the brain stem, where some decussate and others do not
- provide input to lower motor neurons in the nuclei of cranial nerves III, IV, V, VI, VII, IX, X, XI, and XII
- control voluntary movements of the eyes, tongue and neck, chewing, facial expression and speech
Corticobulbar Tract
- also called Cerebrovascular Disease
- cessation of blood flow to the brain due to:
o ruptured blood vessel that bleeds into the brain
o thrombosis of a vessel, producing local ischemia - muscles controlled by the damaged areas show a corresponding loss of function
o clumsiness and loss of fine muscle control
o postural movements may not be affected
o hyperreflexia, hypertonia and spasticity occur with extension of involvement
Strokes
- due to lesions to supplementary and premotor areas
- loss of the ability to prepare for voluntary movement
- ability to execute simple movements is retained
Apraxia
- above the anterior horn cell
- motor neurons that originate in the motor region of the cerebral cortex or the brain stem
- main effector neurons for voluntary movement in layer V of the primary motor cortex (Betz cells)
- UMN pathways (above anterior horn cell) include:
▪ corticospinal tract
▪ corticobulbar tracts
▪ extrapyramidal tracts
Upper Motor Neuron
- below the anterior horn cell
- motor neurons connecting the brainstem and spinal cord to muscle fibers
- bring nerve impulses from the upper motor neurons out to the muscles
- begins at the level of the anterior horn cell in the spinal cord
Lower Motor Neuron
- total loss of motor function associated with an increase in muscle tone
- associated with clasp-knife phenomenon and hyperreflexia
Spastic Paralysis
- total loss of motor function associated with a decrease in muscle tone
- associated with floppiness, areflexia or hyporeflexia
Flaccid Paralysis
- reflex extension of the great toe with flexion of the other toes
- evoked by stroking the lateral sole of the foot
- presence indicates an upper motor neuron lesion
Babinski Reflex
- small, local, involuntary muscle contractions visible under the skin
- arise from spontaneous discharge of a bundle of skeletal muscle fibers
- presence indicates a lower motor neuron lesion
Fasciculations
muscle tone: Increased paralysis: Spastic Paralysis deep tendon reflex: Hyperreflexia babinski sign: Present clonus: Present fasciculations: Absent atrophy: Atrophy of Disuse
Upper Motor Neuron (UMN) Lesion
muscle tone: decreased paralysis: Flaccid Paralysis deep tendon reflex: Hypo/Areflexia babinski sign: Absent clonus: Absent fasciculations: Present atrophy: Atrophy of Denervation
Lower Motor Neuron (LMN) Lesion
- composed of midbrain, pons and medulla
- special functions include:
o control of respiration
o control of the cardiovascular system
o partial control of gastrointestinal function
o control of many stereotyped movements of the body
o control of equilibrium
o control of eye movements
o way station for command signals from higher centers
Brainstem
- activity of the neural circuitry within the spinal cord is modified and refined by descending motor control pathways
o pyramidal tract
▪ CORTICOSPINAL TRACT
o extrapyramidal tracts ▪ RETICULOSPINAL TRACT ▪ VESTIBULOSPINAL TRACT ▪ RUBROSPINAL TRACT ▪ TECTOSPINAL TRACT
Descending Motor Control Pathways
- influence mainly the muscles of the trunk and proximal parts of the limbs
- important in maintenance of certain postures and in startle reactions
- two main divisions
o PONTINE or MEDIAL RETICULOSPINAL TRACT
o MEDULLARY or LATERAL RETICULOSPINAL TRACT
Reticulospinal Tract
- originates in the pontine reticular nuclei
- projects to the ventromedial spinal cord
- general stimulatory effect on both extensors and flexors, with the predominant effect on extensors
Pontine Reticulospinal Tract
- originates in the medullary reticular formation
- projects to spinal cord interneurons in the intermediate gray area
- stimulation has a general inhibitory effect on both extensors and flexors, with the predominant effect on extensors
Medullary Reticulospinal Tract
- originates in Deiters nucleus
- projects to ipsilateral motoneurons and interneurons
- important functions include:
o control the activity of extensor muscles - stimulation causes a powerful stimulation of extensors and inhibition of flexors
o maintenance of an erect posture - selectively controls the excitatory signals to the different antigravity muscles
o making adjustments in response to signals from the vestibular apparatus
Vestibulospinal Tract
- originates in the superior colliculus
- projects to the cervical spinal cord
- decussates before entry to spinal cord - lesions are always contralateral
- important functions include
o control of neck muscles
o controlling head and eye movements
Tectospinal Tract
- most important extrapyramidal tract
- originates in the red nucleus
- afferent information from cortex, cerebellum and basal ganglia
- projects to interneurons in the lateral spinal cord
- decussates before entry to spinal cord - lesions are always ipsilateral
- controls both flexor and extensor muscles
o stimulation of the red nucleus produces stimulation of flexors and inhibition of extensors - voluntary movements are impaired with lesions
Rubrospinal Tract
origin: Pontine reticular nuclei
projection: Ventromedial SC
decussation: None (ipsilateral)
function: Stimulate flexors and extensors
Pontine Reticulospinal tract
origin: Medullary reticular nuclei
projection: Intermediate gray
decussation: None
function: Inhibits flexors and extensors
Medullary Reticulospinal tract
origin: Deiters nucleus
projection: Ventromedial SC
decussation: None
function: Stimulates flexors and extensors
Vestibulospinal Tract
origin: Superior colliculus
projection: Cervical SC
decussation: Yes (Contralateral)
function: Controls neck muscles
Tectospinal Tract
origin: Red nucleus
projection: Lateral SC
decussation: Yes
function: Stimulates flexors, inhibits extensors
Rubrospinal Tract
- involuntary flexion or extension of arms and legs
- occurs when one set of muscles becomes incapacitated while the opposing set is not
- indicates a severe medical emergency requiring immediate medical attention
- two types:
o DECORTICATE RIGIDITY
o DECEREBRATE RIGIDITY
Abnormal Posturing
- involuntary flexion of the upper extremities in response to external stimuli
- arms flexed, hands are clenched into fists, legs extended and feet turned inward
- less severe
Decorticate Rigidity
- involuntary extension of the upper extremities in response to external stimuli
- head is arched back, arms are extended by the sides, and legs are extended
Decerebrate Rigidity
- cause decerebrate rigidity because of the removal of inhibition from higher centers
Lesions Above The Lateral Vestibular Nucleus
- cause decerebrate rigidity because of the removal of central inhibition from the pontine reticular formation
Lesions Above The Pontine Reticular Formation But Below The Midbrain
- result in decorticate rigidity and intact tonic neck reflexes
Lesions Above The Red Nucleus
- also called the “little brain”
- helps control the rate, range, force, and direction of movements (synergy)
o sequences motor activities
o monitors and makes corrective adjustments in motor activities while they are being executed - silent area of the brain
o electrical excitation does not cause any sensation
o damage does not produce paralysis
Cerebellum
Anatomy of the Cerebellum
- located dorsal to the pons and medulla and protrudes from under the occipital lobes
- divided into three lobes by two deep fissures
o ANTERIOR, POSTERIOR, FLOCCULONODULAR - cerebellar cortex is actually a large folded sheet (17 x 120 cm) with crosswise folds (folia)
o deep cerebellar nuclei lie deep beneath the folded mass of cerebellar cortex
o from medial to lateral: DENTATE, EMBOLIFORM, GLOBOSE, FASTIGIAL
Brainstem Attachments
- superior cerebellar peduncles to midbrain
- middle cerebellar peduncles to pons
- inferior cerebellar peduncles to medulla oblongata
Somatotopic Organization of the Cerebellum
- vermis and intermediate zone contain a somatotopic map of the body surface
o axial portions of the body lie in the vermis
o limbs and facial regions lie in the intermediate zones - lateral portions of cerebellar hemispheres do not have topographical representations
o receive input signals exclusively from cerebral cortex
o plays important roles in planning and coordinating the body’s rapid sequential muscular activities
Layers of the Cerebellar Cortex
GRANULAR LAYER - innermost layer that contains granule cells, Golgi type II cells and glomeruli
PURKINJE CELL LAYER - middle layer that contains inhibitory Purkinje cells
MOLECULAR LAYER - outermost layer that contains stellate and basket cells, dendrites of Purkinje and Golgi type II cells and parallel fibers (axons of granule cells)
- originate in the inferior olive
- demonstrate complex spikes - action potentials beginning with a strong spike and followed by a trail of weakening secondary spikes
- function in conditioning Purkinje cells (motor learning)
Climbing Fibers
- form the bulk of the input, originating in the cortico-, vestibulo-, reticulo- and spinocerebellar tracts
- demonstrate simple spikes - much weaker short-duration action potentials in Purkinje cells
Mossy Fibers
- largest afferent projections
- originate from the basilar pontine nuclei
Pontocerebellar System
- originate from the inferior olivary nuclei
Olivocerebellar Projections
- originate in spinal cord or medulla
Spinocerebellar Fibers
- originate from brainstem
Reticulocerebellar Fibers
- originate from vestibular nuclei and vestibular apparatus
Vestibular Fibers
- central neurons with fan-shaped dendritic trees
- always inhibitory with GABA as its neurotransmitter
Purkinje Cells
- smallest and most numerous neurons in the brain
- parallel fibers are axons of granule cells
- excitatory input from mossy fibers which use glutamate as its neurotransmitter
Granule Cells
o small interneurons with numerous arborizations
o inhibitory in function
Golgi Type II Cells
o inhibitory star-shaped cells found in superficial cerebellum
Stellate Cells
o inhibitory cells whose axons form baskets around Purkinje fibers and are found in deep cerebellar layers
Basket Cells
o complex of synapses having a mossy fiber at its core
o synapsing with axons of Golgi type II neurons and dendrites of granule cells
Glomerulus
- modulate Purkinje cell output
- all of the cerebellar interneurons are inhibitory EXCEPT granule cells
o granule cells have excitatory input to basket cells, stellate cells, Golgi II cells, and Purkinje cells
o basket cells and stellate cells inhibit Purkinje cells (via parallel fibers)
o Golgi II cells inhibit granule cells, thereby reducing their excitatory effect on Purkinje cells
Cerebellar Interneurons
Output of the Cerebellar Cortex
- Purkinje cells are the only output of the cerebellar cortex
o output is always inhibitory, using GABA as NT - inhibitory output modulates the output of the cerebellum and regulates rate, range, and direction of movement (synergy)
Efferent Signals from the Cerebellum
vermis - projects to fastigial nucleus, vestibular nucleus and reticular formation
intermediate zones - project to globose and emboliform nuclei (interposed nuclei)
lateral hemispheres - project to the dentate nucleus, ventral anterior thalamic nuclei and cerebral cortex
CEREBELLAR PATHWAY
Cortex Pons* Cerebellum Dentate nucleus* Red Nucleus Thalamus Corticospinal tract
o consists of the small flocculonodular lobes
o for control of balance and eye movement
Vestibulocerebellum
o consists of lateral zones of cerebellar hemispheres
o for planning and initiation of movement
Cerebrocerebellum
o consists of vermis and intermediate zones
o for control of rate, force, range, and direction of movement (synergy)
Spinocerebellum
- during nearly every movement, certain muscles must be rapidly turned on and then quick turned off
- made possible by interplay of mossy and climbing fibers and Purkinje cells
Turn On/Turn Off Function
o climbing fibers modify sensitivity to parallel fiber input
o when mismatch between anticipated result of movement and its actual result occurs, climbing fiber input is more vigorous
o as movement is practiced, mismatch declines gradually
Motor Learning
o during any movement, momentum develops and must be overcome to stop the movement
o appropriate learned, subconscious signals from spinocerebellum stop the movement precisely at the intended point
Damping Function
- patient with cerebellar lesion assumes unsteady stance and reeling gait (like a drunk person)
- to compensate, he assumes a broad-based stance and a broad-based gait
Ataxia
- failure to meter the contractions that set the distance of motion
Dysmetria
- inability to perform rapid alternating movements
Dysdiadochokinesia
- failure of a movement to be terminated at a proper time
Past Pointing
- difficulty in maintaining position against sudden unexpected displacement
Overshooting
- slowness and slurring of speech
Dysarthria
- volume of voice varies from low to high from peak to peak
Scanning Speech
- tremor of intentionally maintained head or trunk posture or of a limb suspended in front of the body
Postural, Positional Or Static Tremor
- unsteady oscillations of the head or trunk
Tiutubation
o tremor as a limb approaches its target
o results from cerebellar overshooting and failure of the cerebellar system to “damp” the motor movements
Intention, End-Point Or Kinetic Tremor
-jerkiness of eye movement
o rapid, tremulous movements of the eyes rather than steady fixation
- due to failure of damping by the cerebellum
- occurs especially when the flocculonodular lobes of the cerebellum are damaged
Nystagmus
- decreased tone of the peripheral body musculature on the side of the cerebellar lesion
o results from loss of cerebellar facilitation of the motor cortex and brain stem motor nuclei - shows rag doll appearance
Hypotonia
o involves the anterior cerebellar lobe
o ataxia of the lower limbs only
Anterior (Rostral) Vermis Syndrome
o involves the flocculonodular and posterior lobes
o axial ataxia without extremity ataxia
Posterior (Caudal) Vermis Syndrome
o cerebellar signs lateralized to one half of the body
Cerebellar Hemisphere Syndrome
o bilateral cerebellar signs due to involvement of all cerebellar lobes
Pancerebellar Syndrome
- deep cerebral nuclei involved in motor control
- modulates thalamic outflow to the motor cortex to plan and execute smooth movements
- demonstrates programming functions
o generate basic patterns of movement in response to cues from cortical association areas
Basal Ganglia
Role of Dopamine
- connections between striatum and substantia nigra use dopamine as neurotransmitter
o inhibitory on the indirect pathway (D2 receptors)
o excitatory on the direct pathway (D1 receptors)
o overall action is excitatory
Important Functions of the Basal Ganglia
- Cognitive Control of Motor Activity
2. Timing and Scaling Functions
o most of our motor actions occur as a consequence of thoughts generated in the mind
o major function of the caudate nucleus
Cognitive Control of Motor Activity
o basal ganglia control the speed and size of movement
o posterior parietal cortex is the locus for spatial coordination
o projects heavily to caudate nucleus and explains why timing and scaling functions are lost with basal ganglia lesions
Timing and Scaling Functions
- snake-like or writhing movements of the hand and arm or face
- result from lesions of the globus pallidus
Athetosis
- flailing movements of the extremities
- result from lesions to the sub thalamic nucleus
Hemiballismus
- brief, irregular, non-purposeful movements that are vaguely comparable to dancing
- result from lesions to the corpus striatum (specially on caudate nucleus)
Chorea
- results from widespread destruction of the dopaminergic cells in the substantia nigra
- characterized by:
o cogwheel rigidity
o resting pill-rolling tremor
o slowness or difficulty in initiating movement (bradykinesia, akinesia)
o postural instability (shuffling or fenestating gait)
Parkinson’s Disease
- autosomal dominant genetic disorder caused by CAG trinucleotide repeats
o displays anticipation with succeeding generations - characterized by flicking movements in individual muscles (chorea)
o leads to progressive severe distortional movements - caused by depletion of GABA and acetylcholine from many areas of the brain
Huntington’s Disease
General vs. Special senses
General senses Somatic (Cutaneous) senses - Touch, pressure, vibration, warmth, cold, pain, tickle, itch and proprioception Visceral senses - Stretch, pain, chemo-, osmotic-, baro-
Special senses
Olfaction, vision, taste, hearing and equilibrium
- comes from “Soma” or “Somato” - Greek word which means “body”
- transmits information to the CNS about the state of the body and its contact with the environment
Somatosensory System
Somatosensory system
Sensory receptor cells
↓
Neural pathways
↓
Brain cortex- receive stimuli from the external or internal environment
- Specialized epithelial cells
- Neurons that transduce environmental signals (light, temperature) into neural signals
Sensory receptor cells
- conduct information from the receptors to the brain or spinal cord
Neural pathways
deal primarily with processing the information
Brain cortex
- information processed by a sensory system may or may not lead to conscious awareness of the stimulus
Sensory information
- state of (conscious or unconscious) awareness of external and internal conditions in the body
Sensation
- conscious recognition of sensation
- damaged neural networks may give faulty perceptions
- Phantom limb: sensation of a limb that has been amputated
Perception
- onion-like structures surrounding unmyelinated nerve endings
- found in deep skin layers
- for vibration; tapping
Pacinian Corpuscle
- present in nonhairy skin; encapsulated in connective tissue
- found in superficial skin layers
- superficial touch (flutter and stroking movements)
Meissner’s corpuscle
- encapsulated enlarged nerve endings found in deep skin layers
- for skin stretch
Ruffini’s Corpuscle
- found in superficial skin layers
- for steady pressure and texture
Merkel’s Disk
- found in muscles, joints, tendons
- for position
Propioceptors
Thermoreceptors
Warm receptors - free nerve endings in skin for warm temperature (30-45C)
Cold receptors - free nerve endings found in skin for cold temperature (20-35C)
- free nerve endings found in skin, muscle and viscera for noxious stimuli and extreme temperatures
- receptors for pain
Nociceptors
- Receptors are particularly distinct to a specific type of environmental change and less sensitive to other forms of stimuli
- e.g. Vision receptors – contain pigment molecules that respond to light
Selective Response of Sensory Receptors
Somatic sensation
Tactile sensations - Touch, pressure, vibration, tickle, itch
Themoreceptive sensation - Heat and cold
Pain
Proprioception - Receptors from this sensations comes from the skin, muscles, bones, tendons, and joints
- Mechanoreceptors with nerve endings linked to networks of collagen fibers within a capsule
- Touch, movement, and vibration sensations - Rapid adapting receptors
- Pressure - Slow adapting receptors
Touch-Pressure
- Muscle-spindle stretch receptors in skeletal muscles, mechanoreceptors in the joints, tendon organs (Golgi), ligaments, and skin
- Also supported by vision and the vestibular organs
Posture and Movement
Muscle spindle
- Activity depends on muscle length
- Annulospiral, flower-spray endings
Golgi tendon
- Passive stretch and active contraction increases the tension of the tendon that activate the tendon organ receptor
Stretch Receptors
- Sensitive to changes, not to absolute temperature
- Adapt only between 20° and 40° C
- Stimuli outside this range activate nocireceptors because of the high probability of tissue damage
- Skin thermoreceptors play a role in temperature regulation, which is controlled by centers in hypothalamus
Temperature
- Gradiations of temperature: blue to red
(freezing cold > cold > cool > indifferent > warm > hot
> burning hot) - Cold spots > warm spots: located beneath the skin at discrete “spots”
- Warm receptors- free nerve endings, transmitted thru type c fibers
- Cold receptors- type A delta nerve fibers, some type c
Thermoreceptors
- free nerve endings that are stimulated when there is tissue damage
Pain: Nociceptors
Qualities of Pain
Cutaneous pricking pain: well localized and easily tolerated
Burning pain: poorly localized and poorly tolerated
Deep pain: arising from the viscera, musculature and joints, poorly localized, can be chronic and often associated with referred pain
- Sensitive to a stimuli causing tissue injury
- Chemical mediators include:
Histamine, bradykinin & prostaglandins from site of injury
ATP & 5-HT (serotonin) from platelets activated by injury
Substance P from the primary sensory neurons - At 45°C, pain is perceived in the skin
Nociceptors
- Lactic acid accumulates in the tissues
- Chemical agents formed
- Perception of pain
Tissue ischemia
Effect of mechanoreceptive pain receptors, ischemia
Muscle spasm
Pain from deep structures of the head referred to the surface
Areas that are pain sensitive:
- Venous sinuses
- Tentorium
- Dura at the brain base
- Meningeal blood vessels
- Middle meningeal artery
Headache
Types of Intracranial headache
- Headache of meningitis
- Low CSF pressure headache
- Migraine headache
- Alcoholic headache
- Headache cause by constipation
Severe headache from the inflammation of meninges
Headache of meningitis
- Unknown mechanism
- Starts with a prodrome lasting minutes to an hour
Theories of Migraine headache:
- Vasospasm of the arteries producing ischemia
- Spreading cortical depression
- Psychological abnormalities
- Vasospasm by excess potassium in the ECF
Migraine headache
headache from absorbed toxic products or fluid loss in the gut
Headache caused by constipation
headache due to Alcohol- toxic to tissues
Alcoholic headache
Types of Extracranial headache
- Headache from muscle spasm
- Headache from irritation of nasal and accessory nasal structures
- Headache caused by eye disorders
- Muscle contraction
- Excessive irradiation
- Pain of visceral origin is referred to sites on the skin and follows the dermatome rule
- Sites are innervated by nerves that arise from the same segment of the spinal cord
- E.g. ischemic heart pain is referred to the chest and shoulder
Referred Pain
Causes of true visceral pain (poorly localized pain)
- Ischemia of visceral tissue
- Chemical damage to the visceral surface
- Spasm of hollow viscus smooth muscle
- Overdistention of hollow viscus
- Stretching of tissues surrounding or within the viscera
- sharp, well localized pain
- Visceral disease spreads to parietal peritoneum, pleura or pericardium
- Parietal surface supplied with pain innervation – sharp pain
- Appendicitis - Inflamed appendix pass pain impulses into the spinal cord levels T10 or T11 – referred pain to the umbilicus
Parietal Pain
Sensory Transduction
Action potentials in nerve fibers
↑
Receptor potentials
↑
Transformation of stimulus energyMechanisms of Receptor Potentials
- By mechanical deformation - Stretches the receptor membrane; Opens ion channels
- By application of a chemical - Opens ion channels
- By change of the temperature of the membrane
- Alters the permeability of the membrane
- Central nerve fiber extending through its core.
- Surrounding – multiple concentric capsule layers
- -Compression anywhere on the outside of the corpuscle will Elongate, Indent or Deform the central fiber
- Central fiber of the pacinian corpuscle
- The tip of the central fiber - unmyelinated
- The fiber - Myelinated
- Sodium influx - a local circuit of current flow occurs
- Node of Ranvier - action potentials are transmitted
Pacinian corpuscle: Eliciting an Action potential
- process by which an environmental stimulus activates a receptor and is converted to electrical energy
sensory transduction
- A single afferent neuron with all its receptor endings
Sensory unit
- area subserved by the sensory unit
- overlap so that when 1 point is stimulated it activates several sensory units
- E.g. ice cube on the skin give rise to sensations of touch and temperature simultaneously
- Area of the body when stimulated, changes the firing rate of a sensory neuron
- Large receptive field: less precise perception
- Small receptive field: more precise perception
Receptive field
- Conversion of receptor potentials into action potentials that conveys sensory information to the CNS
- Nature of a sensation and the type of reaction generated vary according to the destination of sensory impulses in the CNS
Sensory Coding
Characteristics of the stimuli
- Type (Modality)
- Intensity
- Location
- Duration
- property by which one sensation is distinguished from another
ModalitIes: Touch-pressure, Posture-movement, Temperature, Pain
Submodalities: Warmth, cold (Temperature)
-The type of sensory receptor activated by a stimulus plays the primary role in coding the stimulus modality
Modality of sensation
Frequency - Increased stimuli, increased action potential
Recruitment - “calling in” or activation of receptors on additional afferent neurons
Intensity of stimulation
True or False
The more the receptor potential rises above the threshold level, the greater action potential frequency
True
- the magnitude of a subjective sensation increases proportional to a power of the stimulus intensity
- the more power the stimulus gives you, the more sensation you feel
- stimulus is directly proportional to sensation
Stevens’ power Law
- the magnitude of a subjective sensation increases proportional to the logarithm of the stimulus intensity
- Very intense stimulation causes progressively less and less additional increase in amplitude of receptor potentials
- Allows the receptors to have an extreme range of response
- From very weak to very intense
- ratio would matter and not the absolute weight
Weber-Fechner Law
-Receptors adapt either partially or completely to any constant stimulus after a period of time.
When a continuous sensory stimulus is applied,
- The receptor responds at a high impulse rate at first
- Then progressively slower rate until
- Finally the rate of action potentials decreases to very few to none at all
Adaptation of Receptors
- Muscle spindle; pressure; slow pain
- Slowly adapting
- Respond repetitively to a prolonged stimulus
- Detect a steady stimulus
Adaptation: Tonic receptors
- Pacinian corpuscle; light touch
- Rapidly adapting
- Action potential frequency declines with time in response to a constant stimulus
- Primarily detect onset and offset of a stimulus
Adaptation: Phasic receptors
- where the stimulus is being applied
- Acuity - precision in locating the stimulus; small receptive field size, more precise localization
Localization of stimuli
receptors are at the edge of a stimulus is strongly inhibited compared to information from stimulus’ center
Lateral inhibition
- Transmit signals in varying frequencies
- Diameter is proportional to conduction velocity
- Labeled line principle
- General and Sensory nerve classification
Sensory Nerve Fibers
Nerve fibers are specific in transmitting only one modality of sensation
Labeled line principle
- Signals are subject to modification at the various synapses along the sensory pathways before they reach higher levels of the CNS
- Information is reduced or even abolished by inhibition from collaterals from other ascending neurons (e.g., lateral inhibition) or by pathways descending from higher brain centers
Control of Incoming Sensory Signals
- Consists of a bundle of 3-afferent sensory neuron chains that run parallel to each other in the CNS and carry information to the cerebral cortex*
- Specific ascending – carry a single type of stimulus
- Nonspecific ascending – different stimuli
Ascending pathway (Sensory)
- Transmit information from somatic receptors pass the brainstem and thalamus into the Somatosensory cortex
- Processing of afferent information does not end in the primary cortical receiving areas but continues to association areas of the cerebral cortex
Specific ascending pathway
- Polymodal neurons – different stimuli
- Convey information from more than one type of sensory unit to the brainstem reticular formation and regions of the thalamus that are not part of the specific ascending pathways
Nonspecific ascending pathway
- Specific regions of the Primary Somatosensory area (postcentral gyrus, posterior to the central sulcus) receive somatic sensory input from different parts of the body
- The major somatosensory areas of the cerebral cortex are SI and SII
Somatosensory cortex
Sensory pathway: Receptors to the Cortex
First-order neurons
Second-order neurons
Third-order neurons
Fourth-order neurons
- Primary afferent neurons that receive the transduced signal and send the information to the CNS
- Cell bodies are in the dorsal root or spinal cord ganglia
First-order neurons
- Located in the spinal cord or brain stem
- Receive information from primary afferent neurons in relay nuclei and transmit it to the thalamus
- Axons may cross the midline in a relay nucleus in the spinal cord before they ascend to the thalamus - sensory information originating on one side of the body ascends to the contralateral thalamus.
Second-order neurons
- located in the relay nuclei of the thalamus
- information ascends to the cerebral cortex
Third-order neurons
- located in the appropriate sensory area of the cerebral cortex
- information received results in a conscious perception of the stimulus
Fourth-order neurons
- Ascending Anterolateral pathway/ Spinothalamic pathway
- Dorsal column pathway
- Pathways cross from the side where the afferent neurons enter the central nervous system to the opposite side either in the spinal cord (Anterolateral system) or in the brainstem (Dorsal column system)
Neural pathways of the Somatosensory system
- Fine touch, pressure, two-point discrimination, vibration, and proprioception
- Consists primarily of group II fibers
Course:
- Primary afferent neurons: cell bodies in the dorsal root, axons ascend ipsilaterally to the nucleus gracilis and nucleus cuneatus of the medulla
- Second-order neurons cross the midline and ascend to the contralateral thalamus
- Third-order neurons ascend to the somatosensory cortex, where they synapse on fourth-order neurons
Dorsal column system
- Temperature, pain, and light touch
- Group III and IV fibers enter the spinal cord and terminate in the dorsal horn
Course:
- Second-order neurons cross the midline to the anterolateral quadrant of the spinal cord and ascend to the contralateral thalamus
- Third-order neurons ascend to the somatosensory cortex, where they synapse on fourth-order neurons
Anterolateral pathway
- Information from different parts of the body is arranged somatotropically
- Destruction of the thalamic nuclei results in loss of sensation on the contralateral side of the body
Thalamus
- “Little man”
- SI has a somatotopic representation similar to that in the thalamus
- The largest areas represent the face, hands, and fingers, where precise localization is most important.
Sensory homunculus
- Fast pain
- Mechanical (intense pressure), thermal pain stimuli (>45° or
Neospinothalamic tract
- Touch sensations:
- High degree of localization of stimulus.
- Fine graduations in intensity of stimulus.
- Phasic sensations (vibrations)
- Sensations of movement against the skin.
- Fine positional and pressure sensations
Dorsal Lemniscal System
- Thermal sensations: Cold, warm
- Pain sensations
- Crude pressure and touch sensations
- Tickle and itch sensations
- Sexual sensations
Anterolateral Spinothalamic System
- Slow pain
- Polymodal nociceptors (high-intensity persisting mechanical, thermal or chemical stimuli)
- C fiber (group IV)
- Peripheral fibers terminate in the spinal cord almost entirely in laminae II and III of the dorsal horns, which together are called the substantia gelatinosa
- Enters mainly lamina V, also in the dorsal horn
- Join the fibers from the fast pain pathway, passing first through the anterior commissure to the opposite side of the cord, then upward to the brain in the anterolateral pathway
Paleospinothalamic tract
- Loss of sensation and motor function paralysis and ataxia caused by the lateral hemisection (cutting) of the spinal cord
- Pain, temperature sensations lost on the opposite side of the body(Spinothalamic pathway)
- Kinesthetic, position, vibration, discrete localization and two-point discrimination lost on the side of the transection (Dorsal column)
- Crude touch retained
Brown Sequard syndrome
- Chronic disease of the spinal cord characterized by the presence of fluid-filled cavities and leading to spasticity and sensory disturbances
- Generally in the cervical region, with resulting neurologic defects; thoracic scoliosis is often present
Syringomyelia
Parenchymatous neurosyphilis marked by degeneration of the posterior columns and posterior roots and ganglion of the spinal cord
Manifestations
- muscular incoordination
- paroxysms of intense pain
- visceral crises
- disturbances of sensation
- Trophic disturbances, especially of bones and joints(tabes-wasting)
Tabes dorsalis
- Selective suppression of pain without effects on consciousness or other sensations
- Descending pathways selectively inhibit the transmission of information originating in nociceptors -> release certain endogenous opioids -> inhibit the propagation of input through the higher levels of the pain system e.g. morphine
Analgesia
- “Transmission” – turns on gate for pain
- “Inhibitory” cells –shut the gate
- Perception of pain is subject to modulation
Gating Theory of Pain modulation
Analgesia system: Pain suppression in the brain and spinal cord
- Periaqueductal gray and periventricular area of mesencephalon and upper pons
- Raphe magnus nuclei, nucleus reticullaris pargigantocellular
- Dorsal horn of SC – pain inhibitory complex
- Stimulation of higher brain centers that suppress periaqueductal gray area can also suppress pain:
- Periventricular nuclei in the hypothalamus
- Medial forebrain bundle
- Transmitters involved in the Analgesia system:
- Enkephalin – presynaptic and postsynaptic inhibition of type Adelta and C fibers
- Serotonin
- painful site itself or the nerves leading from it are stimulated by electrodes placed on the of the skin
- stimulation of non-pain, low threshold afferent fibers (touch receptor fibers) leads to the inhibition of neurons in the pain pathways
Transcutaneous Electric Nerve Stimulation (TENS)
- Needles are introduced into specific parts of the body to stimulate afferent fibers, and this causes analgesia
- Endogenous opioid neurotransmitters are involved in acupuncture analgesia
Acupuncture
Analgesic drugs
Aspirin - inhibits the synthesis of prostaglandins and slows the transmission of pain signals from the site of injury
Opiates (endogenous opioids: endorphins & enkephalins) - act directly on opioid receptors in the brain, which activate descending pathways that inhibit incoming pain signals
Sensory Pathways for Pain
- Paleospinothalamic tract
- Neospinothalamic tract
Most important Opiate-like substances - stimulate inhibitory neuron so that pain will be less
- Met and leu-enkephalin
- β-endorphin
- Dynorphin
Opiate system
- portion of anterior end of diencephalon that lies below the hypothalamic sulcus and in front of the interpeduncular nuclei
- divided into a variety of nuclei and nuclear areas
- links the nervous system to the endocrine system via the pituitary gland
Hypothalamus
- portion of anterior end of diencephalon that lies below the hypothalamic sulcus and in front of the interpeduncular nuclei
- divided into a variety of nuclei and nuclear areas
- links the nervous system to the endocrine system via the pituitary gland
Hypothalamus
Important Functions of the Hypothalamus
- Endocrine Functions
- Autonomic Functions
- Limbic Functions
___ hypothalamus increase BP and HR
posterior and lateral
part of hypothalamus that decreases BP and HR
preoptic area
- hypothalamus controls the set-point of human body temperature
- controlled by neurons in the preoptic area
- signal appropriate cells to activate body temperature-lowering or temper-ature-elevating mechanisms
Body Temperature Regulation
thirst center of the hypothalamus is the __
lateral hypothalamus
__ release antidiuretic hormone (ADH) into posterior pituitary; controls urinary excretion of water; acts on cortical collecting duct of the kidneys to cause water reabsorption
magnocellular cells in supraoptic nuclei
(hypothalamus)
___ release OXYTOCIN causes contraction of the smooth mus-cle of the uterus and milk let down
magnocellular cells in paraventricular nuclei
(hypothalamus)
______ is responsible for hunger; lesions result in starvation; inhibited by leptin
lateral hypothalamus
(hypothalamus)
___ is the satiety center; activity produces a “stop eating” signal; lesions cause uncontrolled voracious appetite; stimulated by leptin
ventromedial nucleus
(hypothalamus)
__ are involved in reflexes related to food intake like lip licking and swallowing
mamillary nuclei
- hypothalamus elaborates releasing and inhibitory factors that modulate ante-rior pituitary function
- subserved by periventricular zone, ar-cuate nucleus and ventromedial nucle-us
Anterior Pituitary Gland Regulation
Hypothalamus is the __________ of autonomic nervous system; stimulation of the hypothalamus produces autonomic responses
head ganglion
Autonomic Functions of the Hypothalamus
sympathetic: posterior hypothalamus - has a warming function
parasympathetic: anterior hypothalamus - has a cooling function
• stimulation of hypothalamus affects behavioral control functions
Limbic Functions of the Hypothalamus
__ hypothalamus causes increased general level of activity leading to rage and aggression
lateral
(hypothalamus)
__ causes sense of tranquility, pleasure and reward
ventromedial nucleus
(hypothalamus)
__ evokes fear and feelings of punishment and aversion
periventricular nuclei
sexual arousal from __ of the hypo-thalamus
most anterior and most posterior portions
o cycles of periodicity shorter than 24 hours
o examples: heart
Ultradian Rhythms
- cycles of periodicity longer than 24 hours
- examples: menstrual cycle, gestation
Infradian Rhythms
- cycles of periodicity that approximate Earth’s rotational period (24-hour day)
- examples: sleep-wake cycle, hormone levels
Circardian Rhythms
- regulate activity of many physiological processes including heart rate, blood pressure, body core temperature and blood levels of hormones
- external environmental clues influence strict 24-hour cycles
Biological Clock
• implicated in regulation of circadian rhythms
• secretes a hormone called melatonin that is synthesized from serotonin
o increased during darkness
o inhibited by daylight
o controlled by sympathetic nerve activity, which is regulated by light signals from the retina
Pineal Gland
- also known as jet lag
- physiological condition which results from altera-tions of circadian rhythms
- when traveling across time zones, body clocks will be out of synchronization with the destination time - due to experience of daylight and darkness contrary to accustomed rhythms
- treated with melatonin or sunlight exposure
Desynchronosis
• unconsciousness from which the person can be aroused by sensory or other stimuli
Sleep
Types of Sleep
- Slow Wave Sleep / Non-REM Sleep
* Rapid Eye Movement (REM) Sleep
- deep, restful type of sleep
- characterized by decreases in periph-eral vascular tone, blood pressure, respiratory rate and metabolic rate
- frequently called dreamless sleep
- however, dreams and sometimes even nightmares do occur during slow-wave sleep
Slow Wave Sleep / Non-REM Sleep
- called paradoxical because the brain is active and skeletal muscle contractions occur
- lasts 5 to 30 minutes
- repeats at 90 minute intervals
- may be absent in extremely tired individuals
Rapid Eye Movement (REM) Sleep
Important Characteristics of REM sleep
• active form of sleep associated with dreaming and active bodily muscle movements
• more difficult to arouse than slow-wave sleep
• muscle tone is exceedingly depressed
• irregular heart rate and respiratory rate (dream state)
• irregular muscle movements do occur
• brain is highly active in REM sleep
– overall brain metabolism increased by 20 percent
– EEG shows a pattern similar to wakefulness
• raphe nuclei in lower pons and medulla - most conspicuous stimulation area for causing almost natural sleep
• nucleus of the tractus solitarius
• diencephalon
- rostral hypothalamus (suprachiasmal area)
- diffuse nuclei of thalamus
Sleep Centers: Slow-Wave Sleep
What neurotransmitter is elaborated from raphe nuclei?
Serotonin
Which Cranial Nerves arse subserved by the nucleus tractus solitarius?
- Facial Nerve
- Glossopharyngeal Nerve
- Vagus Nerve
- drugs that mimic the action of acetylcholine increase the occurrence of REM sleep
- gigantocellular cells
- large acetylcholine-secreting neurons in the upper brain stem reticular formation
- postulated sleep center for REM sleep
Sleep Centers: REM sleep
Postulated Functions of Sleep
- neural maturation
- facilitation of learning or memory
- cognition
- conservation of metabolic energy
- restoration of natural balance among neuronal centers
- measures voltage fluctuations resulting from ionic current flows within neurons
- recording the brain’s spontaneous electrical activi-ty from multiple electrodes placed on the scalp
- diagnostic applications: epilepsy, coma, brain death
Electroencephalography (EEG)
Types of EEG Waves
- Alpha Waves
- Beta Waves
- Theta Waves
- Delta Waves
- rhythmical waves with a frequency of 8-12 Hz at about 50 mV
- found in normal, awake but resting (eyes closed) individuals
- disappear during deep sleep
Alpha Waves
- occur at frequencies of 14 to 80 Hz with voltage less than 50 mV
- recorded mainly from parietal and frontal regions
- occur when the eyes are opened in the light
- requires intact thalamocortical projections and ascending reticular input to thalamus
Beta Waves
- wave frequencies of 4 to 7 Hz
- occur mainly in the parietal and tem-poral areas in children but may appear in adults during emotional stress
- associated with brain disorders and de-generative brain states
Theta Waves
- all of the waves below 3.5 Hz
- occur during deep sleep, organic brain disease and in infants
- persist in the absence of cortical input from the thalamus and lower brain centers
Delta Waves
- fairly regular pattern of waves at a frequency of 8–13 Hz and amplitude of 50–100 V (alpha waves)
- most marked in the parietal and occipital lobes
- associated with decreased levels of attention
Alpha Rhythm
- alpha rhythm is replaced by an irregular 13–30 Hz low-voltage activity (beta waves)
- also called alpha block, arousal response or desynchronization
- produced by any form of sensory stimulation or mental concentration
Beta Rhythm
- lapsing abruptly into REM sleep from awake state
- sleep episodes last about 15 minutes without warning
- often triggered by a pleasurable event
- emotionally intense experience can also trigger cataplexy, a sudden loss of voluntary muscle control
Narcolepsy
- sleepwalkers arise from slow wave sleep in a state of low consciousness and perform activities that are usually performed during full consciousness
- little or no memory of the incident, as they are not truly conscious
Somnambulism / Sleep Walking
- chronic inability to obtain the amount or quality of sleep needed to function adequately during the day
- most common cause is psychological disturbance
Insomnia
- temporary cessation of breathing during sleep
- loss of muscle tone during sleep allows excess fatty tissue or other structural abnormalities to block the upper air-way
- associated with obesity and made worse by alcohol
Sleep Apnea
• entire neuronal circuitry that controls emotional behavior and motivational drives
• important communicating structures:
- brain stem via the medial forebrain bundle
- hippocampus to mammilary bodies via fornix
Limbic System
- first pathway hypothesized to explain appreciation and expression of emotion
- responsible for linking the experience and the expression of emotion
- cingulate cortex is the seat of emotional experience
- output from the cingulate cortex is conveyed via the fornix to the hypothalamus, where it is trans-lated into the expression of emotion through the autonomic nervous system
Papez Circuit
Functions of Limbic System
5 F’s Fighting Fleeing Feeding Feeling Fucking/Fornicating
- stimulation evokes rage, passivity and excessive sexual drive
- highly hyper excitable - weak stimuli can cause seizures
- lesions cause ANTEROGRADE AMNESIA (inability to form new memories)
- provides signals for consolidation of memory
Hippocampus
• window of the limbic system
- receives neuronal signals from all portions of the limbic cortex, as well as from the neocortex of the temporal, parietal, and occipital lobes
• functions
- endocrine and vegetative functions
- involuntary movements
- rage, escape, punishment, severe pain and fear
- sexual activity
Amygdala
- results from bilateral destruction of the amygdala
- manifestations include
o hyperorality
o loss of fear
o decreased aggressiveness
o changes in eating behavior
o psychic blindness
o excessive sexual drive
Kluver Bucy Syndrome
- most poorly understood portion of the limbic system
* cerebral association area for control of behavior
Limbic Cortex
(Limbic Cortex)
lesions in the bilateral anterior temporal cortex will cause __
Kluver-Bucy syndrome
(Limbic Cortex)
lesion in bilateral posterior orbitofrontal cortex will cause __
insomnia, restlessness
(Limbic Cortex)
lesion in bilateral anterior cingulate and subcallosal gyri will cause __
extreme rage reaction
• acquisition of the information that gives an organism the ability to alter behavior on the basis of ex-perience
• two types:
o ASSOCIATIVE LEARNING
o NON-ASSOCIATIVE LEARNING
Learning
- also called simple learning
- modification of response to a repeated stimulus
- habituation occurs when the response be-comes weaker as the stimulus is perceived to have no particular importance
- sensitization occurs when the response is en-hanced in the even that an unpleasant or otherwise strong stimulus is given
Non-Associative Learning
• involves the ability to make a connection between a neutral stimulus and a second stimulus that is ei-ther rewarding or noxious
• two important examples:
o CLASSICAL CONDITIONING
o OPERANT CONDITIONING
Associative Learning
is a learning process in which behavior is sensitive to, or controlled by its consequences
Operant Conditioning
is a learning process in which an innate response to a potent stimulus comes to be elicited in response to a previously neutral stimulus; this is achieved by repeated pairings of the neutral stimulus with the potent stimulus
Classical Conditioning
• ability to store, retain and recall information and past experiences
• two types:
o EXPLICIT / DECLARATIVE MEMORY
o IMPLICIT / NONDECLARATIVE MEMORY
Memory
▪ associated with consciousness (conscious attention)
▪ dependent on the hippocampus and other parts of the medial temporal lobes
▪ depends on higher-level thinking skills such as influence, comparison, and evaluation
▪ memories can be reported verbally
Explicit/ Declarative Memory
▪ does not involve awareness
▪ retention does not usually involve processing in the hippocampus
▪ acquired slowly through repetition
▪ includes motor skills and rules and procedures
▪ procedural memories can be demonstrated
Implicit/ Nondeclarative/ Reflexive Memory
- stored in the brain by changing the basic sensitivity of synaptic transmission between neurons as a result of previous neural activity
- new or facilitated pathways are called memory traces
Physiology of Memory
- lasts seconds to hours
- memory traces are subject to disruption by trauma and various drugs
Short-Term Memory
- form of short-term memory that keeps information available, usually for very short periods
Working Memory
- stores memories for years and sometimes for life
- long-term memory traces are remarkably resistant to disruption
Long-Term Memory
What type of neuronal circuit is exemplified in short-term memory?
Reverberating Circuit
- initiation of chemical, physical, and anatomical changes in the synapses
- rehearsal enhances the transference of short-term memory into long-term memory
- new memories are codified into different classes of information
- postulated to be a function of the HIPPOCAMPUS
Consolidation of Memory
Physiologic Evidences of Long Term Memory
- increase in vesicle release sites for secretion of transmitter substance
- increase in number of transmitter vesicles released
- increase in number of presynaptic terminals
- changes in structures of the dendritic spines that permit transmission of stronger signals
• condition in which memory is disturbed or lost
• two basic types:
o ANTEROGRADE
o RETROGRADE
Amnesia
- loss of short-term memory
- impairment of the ability to form new memories through memorization
- usually caused by bilateral lesions to the HIPPOCAMPUS
Anterograde Amnesia
- loss of pre-existing memories to conscious recollection
- person may be able to memorize new things but is unable to recall events or identity prior to the on-set
- usually result from lesions to the THALAMUS
Retrograde Amnesia
- right hemisphere is dominant in facial expression, intonation, body language, and spatial tasks
- left hemisphere is dominant with respect to language, even in left-handed people
- information is transferred between the two hemi-spheres through the CORPUS CALLOSUM
Hemispheric Specialization
- human communication is distinguished by its range and subtlety of expression
- vocalization is the production of sound that has no specific meaning
- language consists of a specific vocabulary and a set of rules of expression (syntax)
Language
- located in the inferior frontal lobe of the dominant hemisphere
- processes the information received from Wernicke’s area into a detailed and coordinated pattern for vocalization
Broca’s Area (Brodmann Area 44)
- located in posterior superior temporal gyrus of the dominant hemisphere
- concerned with comprehension of auditory and visual information
Wernicke’s Area (Brodmann Area 22)
- bundle of the nerve fibers that connect Wernicke’s area to Broca’s area
Arcuate Fasciculus
- appears to process information from words that are read in such a way that they can be converted into the audito-ry forms of the words in Wernicke’s ar-ea
Angular Gyrus (Brodmann Area 39)
- abnormalities of language functions that are not due to defects of vision or hearing or to motor pa-ralysis
- caused by lesions in the categorical/dominant hemisphere
- most common cause is Cerebrovascular Disease
Aphasia
Types of Aphasia
- Broca’s Aphasia
- Wernicke’s Aphasia
- Conduction Aphasia
- Anomic Aphasia
- Global Aphasia
- lesion in Broca’s area
- also called non-fluent aphasia or expressive aphasia
- speech is slow and words are hard to come by
- patients with severe damage to this area are limited to two or three words
Broca’s Aphasia
- lesion in Wernicke’s area
- also called fluent aphasia or receptive aphasia
- speech is normal
- patients talk excessively (jargon, neologisms)
- fails to comprehend the meaning
Wernicke’s Aphasia
- lesion in ARCUATE FASCICULUS
- patients can speak relatively well and have good auditory comprehension but cannot put parts of words together or conjure up words
Conduction Aphasia
- lesion in ANGULAR GYRUS (written words)
- no difficulty with speech or the understanding of auditory information
- trouble understanding written language or pictures
- visual information is not processed and transmitted to Wernicke’s area
Anomic Aphasia
- due to generalized brain destruction
- more than one form of aphasia is often present
- speech is scant as well as nonfluent
Global Aphasia
