L03.2 - Sensory System

Free nerve endings

Simple, branching sensory receptors found in skin, muscle, joints, and viscera that encode information about temperature, touch, itch, and pain.

Spinothalamic pathways

Neural pathways that carry sensory signals from free nerve endings to the brain, involving 1st, 2nd, and 3rd order neurons located in the dorsal root ganglion, spinal cord, and thalamus.

Somatosensory cortex

Brain region where sensory signals from free nerve endings are processed, leading to awareness of sensations and involving motor and sensory cortices for motor control, spatial discrimination, and sensory input.

Direct spinothalamic pathway

Neural pathway that directly transmits sensory signals to the primary somatosensory cortex, enabling better spatial discrimination and involving cortical areas like the homunculus.

Indirect spinothalamic pathway

Neural pathway that involves limbic system association cortices, hypothalamus, and reticular formation, leading to poorer spatial discrimination and involving autonomic centers in the brainstem.

How do sensory signals get to the brain?

• Network of neurones carry sensory signals to the brain. Then develop awareness of the sensation.

Where is the 1st order neuron

Sensory cell body in dorsal root ganglion

Where is the 2nd order neuron

cell body in dorsal born of spinal cord

Where is the 3rd order neuron

cell body in thalamus

Free nerve ending activation

1. Temperature, stretch, touch, pressure

2. Nociceptive signal (danger/damage/impending damage)

3. Inflammatory chemicals

What happens when an action potential arrives at spinal cord

• Synapse passes sensory signal to second order neuron

• Spinal ganglion AKA dorsal root ganglion

What happens at the thalamus

• Second order neurones synapses with the third order neuron in the thalamus

• Finally, the sensory signal is carried to the somatosensory cortex

Motor cortex somatic

motor control of skeletal muscle and general motor planning

Sensory cortex

input from skin, input from proprioceptors and spatial discrimination