In-depth Notes on Brain Function and Spinal Cord Anatomy

How the Brain Records, Processes, and Uses Information

• Overview of brain function in recording, processing, and using information.

Spinal Cord Hemisection: Functional Consequences

• Brown-Séquard Syndrome: A condition resulting from a spinal cord lesion leading to loss of motor function on one side and sensory loss on the opposite side.

Organization of the Spinal Cord Gray Matter

• Structure:
  • Divided into horns (dorsal, ventral, lateral).
  • Contains neuronal cell bodies and synapses.

Major Ascending and Descending Tracts

• Ascending Tracts: Responsible for sending sensory information to the brain. Examples include:

  • Dorsal Column-Medial Lemniscal Pathway: Carries fine touch and proprioception.
  • Spinothalamic Tract: Carries pain and temperature sensations.

• Descending Tracts: Involved in motor control. Key pathways include:

  • Corticospinal Tract: Carries signals from the brain to muscles.
  • Decussation occurs in the medulla for some fibers (lateral corticospinal tract), while others do not cross (ventral corticospinal tract).

Ascending Sensory Pathways

• Paths through Neurons:
  • First-order neurons: Carry signals from receptors to the spinal cord.
  • Second-order neurons: Relay signals to the thalamus.
  • Third-order neurons: Relay signals from the thalamus to the cortex.

Sensory Receptors and Pathways

• Types of sensory receptors:

  • Interoreceptors: Monitor internal body conditions.
  • Exteroreceptors: Respond to external stimuli.

• Different types include:

  • Somatosensory: Pressure, temperature.
  • Visual: Photons.
  • Olfactory: Soluble molecules.
  • Gustatory: Tastants.
  • Hearing: Air waves.
  • Balance: Motion.

Hearing: Cranial Nerve Functionality

• Cranial Nerve VIII (Vestibulocochlear Nerve):

  • Afferent fibers from hearing and equilibrium receptors.
  • Primarily sensory with minor motor components.

• Protection Mechanisms from Loud Noises:

  • Muscles (tensor tympani and stapedius) contract reflexively.

Pain Perception

• Pain nociception:

  • Detected by non-encapsulated nerve endings, abundant in epithelium and connective tissues.
  • Triggered by extreme pressure, temperature, and chemicals.

• Visceral Pain: Stimulated by internal organ receptors, often perceived as referred pain (e.g. heart attack pain felt in the left arm).

Control of Heart Rate by Brain

• Autonomic Nervous System (ANS): Involves both sympathetic and parasympathetic control:
  • Parasympathetic (Vagus Nerve): Decreases heart rate.
  • Sympathetic: Increases heart rate.

Micturition Control in Infants and Adults

• Visceral Reflex Arcs: Involved in bladder control, initiated by sensory input from the bladder stretching.

• Components of Reflex Arcs: Include sensory input, integration center, motor neuron.

• Parasympathetic Control: Promotes bladder contraction, while sympathetic control aids relaxation.

Reflex Arc Components

• Afferent impulses from stretch receptors lead to the detrusor muscle contraction and sphincter control, regulated by higher brain centers based on physiological status.