L03.2 - Sensory System

Free nerve endings

  1. Mostly found in the skin, muscle, joints, viscera.

  2. Temperature, crude touch, itch, nociception (sensing and encoding noxious stimuli)

  • Encode information about temperature etc

  • Structurally simple

  • Branching

  • Penetrate dermis (skin) to sense what is going on

Diversity of sensory receptors

These sensory signals need to get to the brain

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

  1. 1st Order neuron (nociceptor) - sensory cell body in dorsal root ganglion

  2. 2nd Order neuron - cell body in dorsal born of spinal cord

  3. 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

Signal (action potential) arrives at spinal cord

  • Synapse passes sensory signal to second order neuron

  • Spinal ganglion AKA dorsal root ganglion

Thalamus

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

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

Motor and sensory cortices

Motor cortex somatic - motor control of skeletal muscle and general motor planning

Sensory cortex - input from skin, input from proprioceptors and spatial discrimination

Spinothalamic pathways to the brain

Direct spinothalamic

Primary somatosensory cortex

  • Cortical areas

  • Better spatial discrimination

  • i.e. homunculus

Indirect spinothalamic

Limbic system association cortices

  • Limbic system

  • Hypothalamus

  • Reticular formation

  • Reticular activating system

  • Poorer spatial discrimination

Autonomic centres of the brain/brainstem

Reticular formation