Lecture on the Nervous System: Sensory Division

LO

1. Understand the basic morphology of different types of sensory receptors
2. Understand the structure and function of the somatic nervous system
3. Understand the basic structure and function of different types of somatic sensory receptors
4. Understand the structure and function of the primary afferent neurones
5. Understand the function of the efferent division of somatic nervous system
6. Understand the basic structure and function of different special sense receptors and how this sensory information is relayed to the CNS

hard shit:

• special sense - altho got letcures on them later on
• types of alpha motor neurones

Instructor Introduction

• Lecturer: Laura, neuroscience lecturer.
• Focus: Sensory division of the nervous system within human physiology.

Overview of the Nervous System

Organization

• Central Nervous System (CNS):
  • Composed of the brain and spinal cord.
  • Processes and interprets information from the Peripheral Nervous System (PNS).
• Peripheral Nervous System (PNS):
  • Divided into somatic and autonomic nervous systems.
  • Relays sensory information from the periphery to the CNS and motor outputs from the CNS to effector organs.

Sensory and Motor Pathways

• Afferent Pathways: Sensory information to the CNS.
• Efferent Pathways: Motor outputs from the CNS to muscles.
• Somatic Nervous System:
  • Transfers somatic sensory information from the external environment.
  • Regulates voluntary responses (skeletal muscles).
• Autonomic Nervous System:
  • Transfers information from the internal environment (e.g., blood pressure).
  • Regulates involuntary responses (smooth and cardiac muscles).

Sensory Receptors

• Types:
  • Free Nerve Endings
  • Modified Nerve Endings
  • Receptor Cells

Somatic Sensory Receptors

• Mechanoreceptors:
  • Located in the skin.
  • Detect physical distortion (touch).
  • Adaptation varies (rapidly vs. slowly adapting).
• Thermoreceptors:
  • Detect temperature changes.
  • Respond through protein channels (e.g., TRPv1 for hot, TRPM8 for cold).
• Nociceptors:
  • Detect potentially tissue-damaging stimuli.
  • High-threshold free nerve endings.
• Proprioceptors:
  • Detect body position in space.
  • Located in muscles, tendons, and joints.

Sensory Transduction

• Process: Conversion of sensory stimuli into electrical signals (action potentials).
• Receptive Fields:
  • Area where sensory receptors can detect stimuli.
  • Smaller fields = higher sensitivity (e.g., fingers vs. back).

Somatosensory Pathway

• Primary Afferent Neurons:
  • Transmit sensory information from periphery to CNS.
  • Cell bodies located outside the spinal cord.
• Ascending Tracks:
  • Dorsal Column Medial Lemniscus Pathway: Transmits touch and proprioception.
  • Spinothalamic Pathway: Transmits temperature and pain.

Somatosensory Cortex

• Processes sensory information from various body parts.
• Somatosensory Map (Homunculus):
  • Represents body parts in the cortex.
  • Larger areas for highly sensitive regions (e.g., lips, hands).

Motor System Link

• Motor Neurons (Alpha):
  • Transmit motor output from CNS to skeletal muscles.
  • Important for voluntary movement.

Special Sensory Information

Pathways and Receptors

• Taste:
  • Detected by taste receptors cells on the tongue.
  • Transmitted via facial, glossopharyngeal, and vagus nerves.
• Hearing:
  • Detected by hair cells in the inner ear.
  • Transmitted via the cochlear nerve.
• Vision:
  • Detected by photoreceptors in the retina.
  • Transmitted via the optic nerve.
• Olfaction:
  • Odorants detected by free nerve endings in the nasal cavity.
  • Transmitted via the olfactory nerve, bypasses the thalamus.

Summary and Quiz

• Recap of lecture content.
• Quiz on sensory receptor types and pathways.

Conclusion

• Importance of understanding sensory pathways and nervous system function.
• Preparation for next lecture on skeletal muscles and motor pathways.