Sensory and Motor Pathways

Somatic Sensory Pathways The pathways consist of first-order, second-order, and third-order neurons The pathways consist of first-order, second-order, and third-order neurons

Somatic Sensory Pathways The relative size of the area that the somatosensory cortex represents a body part are proportional to the number of specialized sensory receptors The relative size of the area that the somatosensory cortex represents a body part are proportional to the number of specialized sensory receptors

Somatic Sensory Pathways Two Pathways; 1. Posterior Column Pathway to the Cortex 2. Spinothalamic Pathways to the Cortex

Posterior Column Pathway to the Cortex The nerve impulses for conscious proprioception and most tactile sensations ascend to the cortex. The nerve impulses for conscious proprioception and most tactile sensations ascend to the cortex.

Posterior Column Pathway to the Cortex The first neuron goes from the receptor to the cord and ascends to the medulla The first neuron goes from the receptor to the cord and ascends to the medulla

Posterior Column Pathway to the Cortex The second order neuron crosses in the medulla and ascends to the thalamus The second order neuron crosses in the medulla and ascends to the thalamus

Posterior Column Pathway to the Cortex The third order neuron goes to the parietal lobe The third order neuron goes to the parietal lobe

Posterior Column Pathway to the Cortex The posterior columns are damaged by B- 12 deficiency The posterior columns are damaged by B- 12 deficiency

Anterolateral Pathways to the Cortex Carry mainly pain and temperature impulses Carry mainly pain and temperature impulses

Anterolateral Pathways to the Cortex The first order neuron goes from the receptor to the cord and releases substance P The first order neuron goes from the receptor to the cord and releases substance P

Anterolateral Pathways to the Cortex The second order neuron crosses in the cord and ascends to the thalamus (where we become conscious of the pain) The second order neuron crosses in the cord and ascends to the thalamus (where we become conscious of the pain)

Anterolateral Pathways to the Cortex The second order neuron ascends either via the anterior or lateral spinothalamic tracts The second order neuron ascends either via the anterior or lateral spinothalamic tracts

Anterolateral Pathways to the Cortex The third order neuron goes to the parietal lobe where we interpret the pain The third order neuron goes to the parietal lobe where we interpret the pain

Anterolateral Pathways to the Cortex Modulation of pain by the brain: release of substance P is inhibited by descending pathways that release enkephalins Modulation of pain by the brain: release of substance P is inhibited by descending pathways that release enkephalins

Somatic Motor Pathways The primary motor area is the major control region for initiation of voluntary movements The primary motor area is the major control region for initiation of voluntary movements

Somatic Motor Pathways Different muscles are not represented equally in the motor cortex Different muscles are not represented equally in the motor cortex

Somatic Motor Pathways The degree of representation is proportional to the number of motor units in a particular muscle of the body The degree of representation is proportional to the number of motor units in a particular muscle of the body

Somatic Motor Pathways Voluntary motor impulses are propagated from the motor cortex to somatic efferent neurons that innervate skeletal muscles via the direct pathways Voluntary motor impulses are propagated from the motor cortex to somatic efferent neurons that innervate skeletal muscles via the direct pathways

Somatic Motor Pathways Direct pathways; 1. Corticospinal Tracts 2. Corticobulbar Tracts

Corticospinal Tracts They go from the primary motor cortex down through the cerebral peduncles of the midbrain They go from the primary motor cortex down through the cerebral peduncles of the midbrain

Corticospinal Tracts They cross in the medulla (if lateral) or in the spinal cord (if anterior) They cross in the medulla (if lateral) or in the spinal cord (if anterior)

Corticospinal Tracts Then they run down the cord to the anterior grey horn cells where the cell bodies of the lower motor neuron lie Then they run down the cord to the anterior grey horn cells where the cell bodies of the lower motor neuron lie

Corticospinal Tracts Lower motor neurons = somatic efferent neurons Lower motor neurons = somatic efferent neurons

Corticospinal Tracts Efferent = Motor Efferent = Motor

Corticobulbar Tracts Axons of upper neurons run from the primary motor cortex to the corticobulbar tracts in the R. and L. cerebral peduncles of the midbrain Axons of upper neurons run from the primary motor cortex to the corticobulbar tracts in the R. and L. cerebral peduncles of the midbrain

Corticobulbar Tracts The tracts cross and the axons end in the motor nuclei of nine cranial nerves (III, IV,V, VI, VII, IX, X, XI, XII)