HA: Chapter 15

rubrospinal tract

automatically adjusts upper limb position and muscle tone during voluntary movements.

Upper-motor neurons

deliver motor commands to motor nuclei in the brain stem or spinal cord. -exits the cerebral cortex and goes into the brainstem to the spinal cord and exits the ventral root -it can excite or inhibit the lower motor neuron

first-order neuron

is the sensory neuron that delivers the sensations to the CNS; its cell body is in a dorsal root ganglion or cranial nerve ganglion. -goes to the brainstem and synapses with second order

corticobulbar tracts

motor fibers distributed to motor nuclei are grouped in this tract

corticospinal tracts

motor fibers distributed to motor nuclei in the spinal cord form this tract

decussation

of this crossover,

Motor homunculus

on primary motor cortex of left cerebral hemisphere -shows how much motor activity is does. hands and fingers, tongue is big , and the back is pretty small

Lower-motor neurons

relay motor commands from the CNS motor nuclei to skeletal muscle fibers.

Sensory Tracts

-**information enters on the posterior side of the brain** -Sensory receptors monitor conditions inside the body and in the external environment -Complexity of response depends on, where processing occurs and where motor response is initiated -Three main sensory tracts that deliver somatic sensory information to the cerebellar hemispheres. First-order neuron, Second-order neuron, and Third-order neuron -most of the sensory processing happens in the (95% thalamus), spinal cord, and brainstem. -In most cases, the first-order or second-order neuron crosses over to the opposite side of the spinal cord or brainstem as it ascends. As a result, sensory information from the left side of the body is delivered to the right side of the brain, and vice versa.

somatotopic arrangement

-Ascending sensory fibers are arranged within individual tracts according to their site of origin within the body. -Sensory fibers coming from a particular region of the body, such as the upper limb, form a tract containing organized bundles of sensory fibers from the hand, wrist, forearm, and arm.

Motor tracts

-CNS issues motor commands in response to information provided by sensory systems -Commands distributed by: 1. Somatic nervous system: Direct contractions of skeletal muscles 2. Autonomic nervous system: Innervates visceral effectors, such as smooth muscles, cardiac muscle, and glands -85% shift to the opposite side and 15% stays on the same side -**information leaves in the anterior part of brain**

Sensory and Motor Tracts

-Communication between CNS and PNS by nerves, axons, and fibers -Tracts are paired (bilaterally and symmetrically along the spinal cord) -Axons within each tract are grouped according to the body region innervated -Number of synapses varies from one tract to another 1. Sensory tract ending in cerebral cortex involves 3 neurons 2. Sensory tract ending in cerebellum involves 2 neurons

Medial-lateral rule

-Most sensory nerves entering the spinal cord at more inferior levels travel more medially within a Sensory modality arrangement sensory tract than sensory nerves entering the cord at a more superior level. -For instance, a sensory nerve that enters the cord at T11 (11th thoracic spinal nerve) is located more medially within a sensory tract than a nerve that enters at C4. -inferior info is more medial and superior is more lateral

Sensory modality arrangement

-Sensory fibers are arranged within the spinal cord according to the type of sensory information carried by the individual neurons. -ex: information dealing with fine touch will be carried within one sensory tract, while information dealing with pain will be carried within another. -sensory fibers carrying fine touch, pressure, proprioception, and vibration are in the posterior part, pain, temp are lateral part, and crude touch is in the anterior part of spinal cord

motor tracts 2

-Somatic motor tracts always involve at least two motor neurons: an upper-motor neuron, whose cell body lies in a CNS processing center, and a lower-motor neuron located in a motor nucleus of the brain stem or spinal cord. -Activity in the upper-motor neuron can excite or inhibit the lower-motor neuron. -The axon of the lower-motor neuron extends to skeletal muscle fibers, and it is only capable of exciting skeletal muscle fibers.

Second-Order Neuron

-The axon of the first-order neuron synapses on a second-order neuron. -its located in either the spinal cord or the brain stem. -goes to the thalamus

reticulospinal tract

-The functions of the tract vary depending on which area of the reticular formation is stimulated.

somatic nervous system (SNS)

-an upper motor neuron in the CNS controls a lower-motor neuron in the brain stem or spinal cord. -The axon of the lower-motor neuron has direct control over skeletal muscle fibers. -Stimulation of the lower- motor neuron always has an excitatory effect on the skeletal muscle fibers. -upper start in the cortex and they can end at the brainstem or spinal cord to access skeletal muscle -second order is a lower motor

Motor Tracts Carrying Conscious Motor Commands

-anterior corticospinal tract contains axons that do not cross over (decussate) in the brain stem. -The lateral corticospinal tract contains the motor fibers that decussate within the brain stem. -starts in the cerebral cortex (primary motor cortex) and ends at the spinal cord

a third-order neuron

-at the cerebral cortex, the second-order neuron synapses on a third-order neuron in the thalamus. -carries the sensory information from the thalamus to the appropriate sensory area of the cerebral cortex. -according to the area where it arrives on the cerebral cortex is related to the specific sensations

posterior columns

-deliver fine-touch, vibration, and proprioception information to the primary sensory cortex of the cerebral hemisphere on the opposite side of the body. -The crossover occurs in the medulla (brainstem), after a synapse in the nucleus gracilis or nucleus cuneatus.

Anterior spinocerebellar tracts

-first order neurons: Dorsal root ganglia; axons enter CNS in dorsal roots -second order: posterior gray horn; axons enter anterior spinocerebellar tract on same or opposite side -third order: Not present -final destination: Cerebellar cortex, primarily on side of stimulus -crossover: Axons of most second-order neurons cross before entering tract and then cross again within cerebellum

Posterior spinocerebellar tracts

-first order neurons: Dorsal root ganglia; axons enter CNS in dorsal roots. -sencond order neurons: posterior gray horn; axons enter on same side -third order: Not present -final destination: Cerebellar cortex on side of stimulus -crossover: None

Lateral spinothalamic tracts

-first order neurons; Dorsal root ganglia; axons enter CNS in dorsal roots and enter posterior gray horn -second order neurons; In posterior gray horn axons enter lateral spinothalamic tract on contralateral side -third order; Ventral posterolateral nucleus of thalamus -final destination: Primary sensory cortex on side opposite stimulus -site of cross over; Axons of second order neurons, at level of entry -carries sensations of pain and temperature to the primary sensory cortex on the opposite side of the body. The crossover occurs in the spinal cord, at the level of entry.

Anterior spinothalamic tracts

-first order neurons; Dorsal root ganglia; axons enter CNS in dorsal roots and enter posterior gray horn -second order neurons; in the posterior gray horn axons enter on opposite side -every other step is the same as the lateral spinothalamic -carries crude touch and pressure sensations to the primary sensory cortex on the opposite side of the body. The crossover occurs in the spinal cord at the level of entry.

Sensory homunculus

-primary sensory cortex of left cerebral hemisphere -sensitive areas are lips, and fingers are lateral in the cerebral cortex -limbs are located medially in the cortex but lateral in the body

Motor Tracts Carrying Subconscious Motor Commands

-rubrospinal tract: Red nuclei of mesencephalon - reticulospinal: originates in the reticular formation, a diffuse network of neurons in the brain stem. - tectospinal tract: starts at Tectum ends at Lower-motor neurons of anterior gray horns (cervical spinal cord) -vestibulospinal tract: begins at the Vestibular nucleus (at border of pons and medulla oblongata) and ends Lower-motor neurons of anterior gray horns of spinal cord -end at the spinal cord

Neuron Arrangement within Sensory Tracts Neurons

-sensory tracts are not randomly arranged. Rather they are segregated, by at least three anatomical principles: -Sensory modality arrangement, Medial-lateral rules, and somatotopic arrangement

autonomic nervous system (ANS),

-the axon of a preganglionic neuron in the CNS controls ganglionic neurons in the periphery. -Stimulation of the ganglionic neurons may lead to excitation or inhibition of the visceral effector innervated. -starts lower in the hypothalamus goes down brainstem or spinal cord -effects glands, smooth muscle,cardiac muscle, and adipocytes

Major Sensory Ascending tracts

1. *Posterior Columns* starts in the posterior side of spinal cord and ends at the thalamus 2.*Posterior spinocerebellar tract* and *Anterior spinocerebellar tract* ends in the cerebelum 3. *Lateral spinothalamic tract* and *Anterior spinothalamic tract* ends in thalamus

descending tract

Conscious and subconscious motor commands control skeletal muscles through descending motor tracts within the spinal cord.