Spinal Cord and Nervous System Overview

Central hub for directing impulses between the body and the brain.
Involved in spinal reflexes, which are automatic and subconscious responses, maintaining homeostasis by regulating heart rate, blood pressure, swallowing, etc.

Reflex Definition: An automatic response that occurs without conscious control; part of maintaining body homeostasis.
Components of a Reflex Arc:
- Sensory Receptor: Detects stimulus (e.g. heat, pain).
- Interneuron: Processes information within the spinal cord.
- Motor Neuron: Transmits signal to effector (muscle/gland) for response.

Monosynaptic Reflex: Involves one sensory neutron and one motor neutron (e.g. patellar reflex).
- Patellar Reflex Example: Tapping the patellar tendon causes quadriceps muscle to contract and knee to extend, helping maintain posture.
Polysynaptic Reflex: Involves multiple neurons; includes one or more interneurons (e.g. withdrawal reflex).
- Example: Stepping on a painful object causes withdrawal from stimulus for protection.

Diagram Description:
- Green pathway: Sensory neuron bringing information to spinal cord.
- Blue part: Interneuron in spinal cord.
- Pink part: Motor neuron sending signal to muscle.
Functionality: Sensory signals processed in central nervous system (CNS) can lead directly to a motor response.

Ascending Tracts: Carry sensory information from the body to the brain (e.g., spinothalamic tract).
Descending Tracts: Carry motor commands from the brain to the body (e.g., corticospinal tract).

Depends on location and extent of injury; cervical injuries impact body below the neck while lower lumbar injuries impact legs.
CNS neurons do not regenerate; damage leads to loss of sensation or motor function depending on tract affected.

Cranial Nerves: Arise directly from the brain (12 pairs).
- Include sensory (olfactory, optic), mixed, or motor nerves.
Spinal Nerves: Arise from spinal cord and are always mixed (contain both sensory and motor fibers).

Divisions:
- Sympathetic Division: Prepares body for acute stress (fight or flight).
- Parasympathetic Division: Promotes rest and digestion (rest and digest).
Key Functions: Regulates internal organs, heart rate, digestion, response to stress, etc.
Neurotransmitter Functions: Different neurotransmitters involved in sympathetic and parasympathetic responses (e.g., norepinephrine in sympathetic, acetylcholine in parasympathetic).

Decrease in brain size and neuron count, particularly in the frontal cortex as one ages.
Slower reflexes, diminished memory capacity, and slow executive function noted in older populations.

Understand the functions and responses governed by the spinal cord and reflex arcs.
Know critical reflex types (monosynaptic and polysynaptic), the significance of ascending and descending tracts, and their roles within the nervous system.
Recognize differences in spinal and cranial nerves along with the autonomic nervous system's dual functions.