Lesson 3- Reflex Arc

The spinal cord has varying amounts of gray matter and white matter depending on the region.
A cross section reveals an "8 shape" in the middle, representing the gray matter, surrounded by nerves (afferent and efferent).

Definition: Central region of the spinal cord (butterfly or 'H' shape) where synapses occur.
Function:
- It serves as the decision-making area for routing signals:
  - Sensory neurons connect through synapses in gray matter.
  - Synapse: Connection between presynaptic and postsynaptic neurons.
  - Responsible for routing signals either to higher brain centers or reflex arcs (directing towards effectors like muscles).
Gray matter is crucial for processing connections between neurons.

Definition: The outer region of the spinal cord that contains myelinated axons.
Function: Acts as highways for nerve signals to travel:
- Information is routed up (to the brain) or down (to effectors).
- Comprises various tracts (bundles of nerves).
White matter integrates and forwards signals processed in the gray matter.

Dorsal Side: Receives sensory information from the body through afferent neurons.
- Afferent Neurons: Transmit sensory signals to the spinal cord.
- Dorsal root neurons enter the spinal cord carrying information about changes in environment (pressure, temperature, pain).
Ventral Side: Sends motor information to effectors (muscles/glands) through efferent neurons.
- Efferent Neurons: Carry outgoing signals from the spinal cord to effectors.

Dorsal Gray Horn: Receives sensory information (has a horn-like appearance).
Ventral Gray Horn: Sends motor commands to effector tissues.
There may also be Lateral Gray Horns in certain regions, playing similar roles.

Definition: Neural pathways that allow for immediate responses, bypassing the brain.
Mechanism: Directly connects sensory neurons to motor neurons via an interneuron within the spinal cord:
- Sensory information is received through afferent pathways and processed in gray matter.
- Often leads to immediate motor response to prevent injury (e.g., pulling back from a hot surface).
Interneurons: Relay signals between sensory and motor neurons in the reflex arc, facilitating rapid reflex actions without brain involvement.

Neurons can have long axons, making them susceptible to damage.
Ganglion: Nerve cell bodies located outside the spinal cord (for sensory neurons).
Dorsal Root Ganglion: Houses the cell bodies of sensory neurons, leading to the spinal cord.
- Total of 31 pairs of root nerves emerge from the spinal cord for sensory and motor functions.

Reflex tests (e.g., using a reflex hammer) demonstrate how quickly the nervous system can respond without convoluted processing through the brain.
Understanding this mechanism is crucial for studying neurological function and diagnosing issues.