from spinal cord to innervated muscle

exits the ventral horn of the spinal cord

from brain to spinal cord

from primary motor cortex to spinal cord

involves the corticospinal tract (crosses in the pyramids of the medulla)

motor neurons innervating flexors

vs

motor neurons innervating extensors

• directly trigger the generation of force by a muscle
• release ACh at neuromuscular junction

innervate intrafusal fibers within muscle spindle

proprioceptive informations and feedback from muscles

Dorsal Root Ganglion- feedback about muscle length

Upper Motor Neurons- control of voluntary movement

Interneurons- generation of motor programs

1. Varying firing rate of motor neurons
2. Recruitment fibers

• alpha motor neurons release ACh
• one EPSP from ACh to nicotinic receptors = one action potential
• one AP= one muscle twitch (contraction and relaxation)
• Rate of AP= graded muscle contraction

• excitable cell membrane surrounding muscle fiber
• location of motory neuron synapse
• made up of two Z lines and a myofibril

• stretch receptor (proprioceptor)
• senses muscle length
• associated with A alpha (1A) sensory neurons
• when stretched leads to depolarization of A alpha axon endings = increased firing of A alpha = increased AP discharge
• as muscle is slackened discharge rate decreases (as muscle is stretched discharge rate increases)

• modified skeletal muscle fibers in muscle spindles
• innervated by Gamma motor neurons
• contract in response to shortening of extrafusal fibers

• acts as a strain gauge
• monitors muscle tension or the force of contraction
• innervated by 1B axons
• in series with the muscle

• sensory neurons synapse of alpha motor neurons
• muscle spindles stretched=increase of AP discharge of 1A axons
• muscle spindle slackens= decrease in AP discharge of 1A axons
• ex. Knee jerk reflex

tap stretches quad-> 1A fiber causes reflex contraction and extends leg

• Monosynaptic

• provides feedback aboud muscle tension
• protects muscle form being overloaded
• Normal: regulate muscle tension in an optimal range
• Beta axon from golgi tendon axon innervates inhbitory interneuron in spinal cord-> inhibition of alpha motor neuron and a decrease in muscle contraction
• Polysynaptic

Reciprocal Inhibition

contraction of one set of muscles is coupled to the relaxation of antagonistic muscles

A alpha sensory axon causes stimulation of alpha motor neuron (flexor) and relaxation of the extensor

Flexor Reflex

• reflex arc to withdraw limb from averse stimulus
• building block for locomotion
• pain axon innervates alpah motor neurons to cause flexon of that muscle: inhibits antagonist muscle
• pain axons entering spinal cord branch to activate interneurons at various spinal segments-> excites motor neurons that contrl flexor muscles of the affected muscle
• ex reflex allows you to keep standing even when one leg is hurt (step on tack)

• high level of motor control
• planning movement, goal directed movements
• associated with basal ganglia and association areas of the neocortex---- prefrontal cortex and striatum

• middle level of motor control
• spatial and temporal arrangement of sequence of muscle contractions
• triggered by motor cortex and cerebellum

• low level of motor control
• activation ofmotor neuron and muscle contraction
• cannot be modified without sensory info or higher input
• associated with brain stem and spinal cord

• Lateral Pathways- control voluntary movements of distal musculature
• Ventromedial Pathways- control postural musculature

• descending motor tracts
• voluntary movements of distal musculature
• innervation to flexor muscles

• descending motor tracts
• originate in brainstem- uses sensory info about balance and position
• unconscious control of postural musculature

• lateral pathway
• originates in motor cortex
• crosses in pyramids
• innervate alpha motor neurons and inhibitory interneurons

• originates in red nucles
• lateral pathway
• central input from cortex
• crosses in pons
• can compensate for lesion in corticospinal tract

• ventromedial pathway
• originates in vestibular nuclei
• enervated by cranial nerve VIII
• controls neck and back muscles down to lumbar region to facilitate extensor mucles of legs
• bilateral in spinal cord
• medial longitudinal fasiculus carries this tract to the neck and extraocular eye muscles
• No conscious cortical input to the tract, only cerebellar input

• ventromedial pathway
• originates in superior colliculus
• head and neck posture and movement
• eye position

• receives cortical input via the corticoreticular and ascending spinoreticulartracts
• opposite effects of medullary
• enhances the antigravitey reflexes of the spinal cord
• facilitates extensors of the legs and back
• maintains upright position
• excites gamma motor neurons

• receives cortical input via corticoreticular and ascending spinoreticular tracts
• opposite of pontine
• relieve antigravity muscles from reflex control
• inhibits extensors, inhibits gamma motor neurons

• supplementary motor area
• planning and coordination of complex movements
• projects to M1

• Pre-motor area
• projects to M1
• proximal motor unites
• outputs to reticulospinal tract
• stimulation causes sequence of movements
• involved in planning movement

• primary motor cortex M1
• humunculus
• stimulation leads to movement or twitching in arm or limb
• has lowest threshold for elicitation of the movements by electrical stimulation

• skilled voluntary movement
• SMA and PMA

• originates in layer V (betz cells)
• receives input from cortical areas and thalamus and SMA and PMA

• most of the motor cortex is active for every movement
• activity for each cell encodes a choice for a particular movement
• direction of movement is determined by averaging choices

• to thalamus from basal ganglia: part of feedback loop
• facilitates willed movement
• cortex-->Neostriatum-->Globus Pallidus-->VL-->cortex

• inhibits spontaneous movement
• pathway to thalamus from basal ganglia: part of feedback loop
• cortex-->Neostriatum-->Globus Pallidus (lateral) -->Subthalamic-->Globus Pallidus (medial)-->Thalamus--> Cortex

• input to thalamus (VLo)--> area 6
• involved in planned movements

• striatum (putamen, caudate, accumbens)
• globus pallidus (inner, outer, innominata)
• subthalamic nucleus (football shape)
• substantia nigra (pars compacta, reticulata)

• hypokinesia- decreased movement
• bradykinesia- slowed movements
• akinesia- difficulty in initiating willed movements
• rigidity- increased muscle tone
• tremors at rerst

• degeneration of substantia nigra inputs to striatum --> tonic inhibition to thalamus--> continuous excitation of cortex

• hyperkinesia- excessive movement
• dyskinesias- abdormal purposeless movements
• Huntington's Chorea-- spontaneous, uncontrolled movements
• Loss of neurons in caudate/putamen and globus pallidus--> loss of inhibitory inputs to thalamus
• Loss of cortical neurons--> dementia and personality changes

• receives input from spinal cord/brainstem (proprioceptive information) and cerebral cortec (motor ouput coordination)
• sends outputs to thalamus (VL) and brainstem
• outputs to pons-->VL-->Area 4

• coordinated movement
• learning of motor sequences and multi-joint movements
• lesions cause ataxia (inaccurate, uncoordinated movements)

• Vermis: outputs to brainstem to control ventromedial pathways which then control axial muscles
• Hemispheres- controls lateral pathways which control limbs
• Deep cerebellar nuclei- output function

1. Medial (Vermal)
2. Intermediate (Paravermal)
3. Lateral (hemisphere)

• Purkinje
• Granule
• Molecular

• inhibitory inputs from Purkinje cells and collateral excitatory projections from mossy fibers and climbing fibers
• ouput of cerebellum

also known as Interposed nuclei

• associated with paravermal functional zone

• associated with lateral hemispheres of cerebellum

Mossy Fibers

Climbing Fibers

Multilayered Fibers

• originate from deep nuclei, medulla, and pons
• synapse on golgi and granule cells and release glutamate

• from inferior olive
• excitatory
• wrap around dendrites of purkinje cells (multiple synapses on single purkinje cells)

• inputs from locus ceruleus, raphe nuclei and hypothalamus
• inhibitory

• only efferent cells of the cerebellar cortex (only cells to project out of cerebellar cortex)
• release GABA and inhibit cells
• project to deep cerebellar nuclei and vestibular nuclei
• receive inputs from parallel fibers from inferior olive

• composed of granule, golgi, and unipolar brush cells
• Granule cells: axons form on parallel fibers and project up to purkinje cells: excitatory (release glutamate): input from mossy fibers from pons

• closest to the surface
• dendrites for purkinje cells
• basket and stellate cells: both inhibitory

• zone of cerebellum
• equilibrium, eye orienting and position of head and body in space
• damage to flocculonodular lobe ad fastigial nucleus results in unsteady gait, drunken appearance, tendency to fall

• zone of cerebellum
• control of axial musculature through fastigial and vermal cortex and limb musculature through interposed nucleus
• associated with vermis and intermediate zone
• damage results in same symptoms of pontocerebellum and vestibulocerebellar damage

• zone of cerebellum
• preceision and timing of movements of upper extremities
• damage results in decrease of coordinated movement, hypotonia, ataxia, intention tremors

• executive function (fully develops in adolescence)
• decision making and goal seeking behavior
• detect situations taht require mediation
• suppress distractions
• encode motor funtion
• future planning
• integrate memories to execute action
• working memory

• lots of white matter in prefrontal cortex that doesnt connect to rest of brain (autistic behavior)
• found in drug addiction, schizophrenia, ADHD, PTSD, OCD and autism

• Orbitofrontal (OFC)
• Ventrolateral areas (vl-PFC): lesions here eliminates autonomic response to fear
• Dorsolateral prefrontal cortex (dl-PFC): medial prefrontal (anterior and ventral cingulate cortex)

• extensive connections to other brain areas
• access information from sensory areas
• influence on other sensory areas
• short term memory storage
• modifiable
• information about goals and means to achieve them

• areas 8, 9, and 46
• working memory and executive control
• temporal organization of behavior
• sensory info from all 3 modalities and polymodal areas
• area 46- preferential connections with many motor systems: control over motor output connections to Basal Ganglia, but not to M1

• Areas 12 and 45
• attention, vision, recognition, emotional control
• sensory information (visual, somatosensory, auditory) overlapping info from all 3 modalities
• memory
• inputs from polymodal areas
• involved in autonomic fear response
• Wisconsin card sorting Task

• Areas 10, 11, 13, 14
• reward, motivation, emotional decision making
• chemosensory and visceral information
• limbic system connections
• behavioral inhibition over choices based on objects or rewards
• Gambling Task

• brainstem, diencephalon and limbic system: info about internal environment, level of arousal, motivation, visceral outputs of emotion
• Amygdala and hypothalamus to ventral and medial PFC: motivation
• hippocampus

• Broca's Limbic Lobe
• Limbic Lobe (Cingulate Gyrus)
• Hippocampus
• Brainstem Nuclei
• Parahippocampal gyrus

Limbic structures (including cortex) involved in emotion

Emotional system on medial wall of brain linking cortex with hypothalamus

• cortex: emotional experience
• hippocampus: involved in fear and aggression
• Anterior thalamus: lesions lead to spontaneous laughing and crying
• Hypothalamus: governs expression of emotion--> connects to cortex linking experience and expression

• caused by temporal lobectomies
• related to destruction of medial temporal lobe and amygdala
• in monkeys: decreased fear and aggression, increased interest in sex, more explorative (put things in mouth)
• in humans: flattened emotions, less fear, more arousal

• Basolateral: receives input
• Corticomedial: receives input
• Central: provides output

• group of nuclei of amygdala
• sensory systems input from all systems EXCEPT olfactory

• group of nuclei of amygdala
• olfactory system inputs
• involved with hypothalamus

• group of nuclei of amygdala
• brainstem nuclei

• Hippocampus
• Cortex
• Cingulate Gyrus
• Dorsal Thalamus
• Hypothalamus
• Brainstem

• Amygdalofugal
• Stria-terminalis

• express aggression but no action
• elicited by stimulating medial hypothalamus
• more for show--> high levels of sympathetic activation

• expresses aggression and acts on it
• elicited by stimulating lateral hypothalamus
• low levels of sypathetic activation
• usually attacks made against an animal for the purpose of obtaining food

• endocrine system- via pituitary
• ANS- preautonomic cells via brainstem and spinal cord: medial forebrain bundle and dorsal longitudinal fasciculus

• ascending sensory signals from brainstem/spinal cord
• Descending afferents from cortex and limbic system

• integrates sensory, cognitive and emotional information to regulate endocrine, autonomic and behavioral response
• homeostasis

• Periventricular Zone- neurosecretory, ANS funtion
• Lateral Zone- motivation, stress, sex
• Medial Zone- motivation, stress, sex

• Supraoptic nucleus and Paraventricular nucleus- water and electrolyte balance (vasopressin): lactation partuition (oxytocin)
• Paraventricular- stress
• Arcuate and Paraventricular Nuclei- hypothalamic releasing hormons (factors)
• Arcuate- leptin: regulation of body fat and food intake

• outcropping of hypothalamus
• releases oxytocin and vasopressin
• inputs from neurosecretory neurons from Supraoptic and paraventricular Nuclei

• Not part of brain
• Secretes hormones
• utilizes portal blood system

• arcuate and paraventricular nuclei and the lateral hypothalamus

• hormones from stomach and autonomic control via vagus nerve

• decreases feeding behavior
• incresases secretion of TSH and ACTH: acts on thyroid and adrenal glands--> increase of metabolic rate throughout NS

• raises metabolic rate and body temperature

• paraventricular nucleus: secretes TSH and ACTH (both increased secretion)
• PVN and Arcuate neurons control the autonomic NS
• MSH and CART diminish apetite

• stimulates an increase in NPY and AgRP
• NPY and AgRP inhibit secretion of TSH and ACTH    --> stimulates feeding behavior (OREXIGENIC)
• AgRP and MSH bin MC4 receptor: MSH activates MC4 and reducese feeding behavior: AgRP is an antagonist

• FSH- follicle stimulating hormone: ovulation and spermatogenesis
• LH- luteinizing hormone: sperm and ovarian maturation
• TSH- thyroid stimulating hormone: thyroxin secretion for metabolism
• ACTH- Adrenal Corticotropin Hormone: cortisol secretion
• GH: growth hormone: protein synthesis
• Prolactin: growth and milk secretion

• MCH- melanin concentrating hormone: released from cells of lateral hypothalamuc- widespread connections to brain including the cortex (organizes and intiates goal mediated behavior: ie food seeking behavior)
• Orexin- stimulates feeding behavior (also involved in wakefulness and initially used to treat narcolepsy)
• MCH and Orexin levels rise when leptin levels fall

• Mechanical Detection: Gastric distension: vagus nerve: inhibits feeding behavior
• Ghrelin: released into bloodstream when stomach is empty- activates AgRP and NPY- stimultes feeding behavior
• CCK- cholecystokinin: released in response to intestinal stimulations with fatty foods- acts at sensory neurons of vagus nerve