Chapter 15 A&P lecture

Chemical Nature of Neurotransmitters

• Neurotransmitters are classified as chemicals.

• Example: Acetylcholine is a neurotransmitter and hence a chemical.

• The responsibility of neurotransmitters is to open chemically gated channels.

Neurotransmission and Action Potentials

• Inhibition causes hyperpolarization, meaning the cell's internal environment becomes more negatively charged.

• Hyperpolarization is achieved by opening potassium channels, rather than sodium channels.

• It’s essential to understand these relations for exams, as questions may be phrased differently but test the same concepts.

Reflexes and Classification

• Reflexes can be classified as innate or learned based on their development.

• Reflex processing locations: spinal cord and brain (cranial processing).

• Motor responses can be somatic (voluntary) or visceral (involuntary).

• The complexity of reflex pathways can indicate if they are polysynaptic (more than one synapse involved).

Importance of Study Habits

• With limited time before exams, consistent study behavior is crucial.

• Engage in office hours to clarify doubts and improve understanding.

• Focus on completing quizzes and lecture tests to maintain a good overall grade.

Sensory Pathways in the Nervous System

• Afferent vs. Efferent Division:

  • Afferent division is responsible for sensory information coming into the central nervous system.

• Sensory input involves sensing through receptors and sensory neurons, which sends action potentials to the central nervous system.

• The brain processes this information to produce motor outputs.

• Only about 1% of sensory information reaches our conscious perception.

General vs. Special Senses

• General Senses include temperature, pain, touch, pressure, vibration, and proprioception.

• Proprioception pertains to the awareness of body position and movement.

• Special Senses (discussed in Chapter 17) have specific receptors for smell, taste, sight, sound, and balance.

Receptive Fields

• Receptive fields refer to areas where sensory receptors can detect stimuli.

• Larger receptive fields offer less precision (e.g., back), while smaller fields allow for precise localization (e.g., fingertips).

• The pattern of action potentials dictated by the type of touch influences the perception of materials.

Types of Receptors

• Receptors are specific: each receptor type is designed to respond to a specific kind of stimulus (e.g., you can't see with your ears or feel with your eyes).

• Tonic Receptors: always active, respond to constant stimulus changes. Example: blood pressure receptors.

• Phasic Receptors: adapt quickly to unchanged stimuli, providing rapid responses. Example: touch and temperature receptors.

Interneurons and Pathway Information

• Sensory information can reach awareness and be processed by the brain through interneurons.

• Neuronal pathways can be classified into several categories:

  • Spinothalamic Pathway: carries pain and temperature sensations; includes first, second, and third order neurons.

  • Posterior Column Pathway: associated with touch and proprioception.

  • Spinocerebellar Pathway: provides proprioceptive information to the cerebellum without reaching conscious awareness.

• Understanding these pathways helps in diagnosing and treating sensory system issues.

Pain and Temperature Sensations

• Nociceptors: pain receptors that respond to various types of damage (thermal, chemical, mechanical).

• Pain sensations are categorized into fast pain (sharp, immediate response) and slow pain (dull, lingering).

• Thermoreceptors: detect temperature changes; important for body temperature homeostasis.

Mechanoreceptors and Proprioceptors

• Respond to mechanical changes (pressure, vibration).

• Includes tactile receptors for touch, baroreceptors for pressure in blood vessels, and proprioceptors for muscle position awareness.

Sensory Integration

• Different types of sensory information converge in the brain to create a comprehensive perception.

• This involves a complex network of neuronal pathways and specific brain regions (e.g., sensory cortex) inferred from action potentials sent from sensory neurons.

Final Notes on Sensory Systems

• The sensory homunculus is a visual representation of the area of the cortex dedicated to different sensory regions, highlighting the disproportionality of sensory receptors in body parts.

• Be aware that studying these connections can prepare students for practical applications in various healthcare settings.