Human Biology: Central Nervous System

Central Nervous System Lecture Outline

• The central nervous system (CNS) is composed of the brain and spinal cord
• The CNS receives input from sensory neurons and directs activity of motor neurons that innervate muscles and glands
• Association neurons integrate sensory information and regulate homeostasis and responses to the environment
• The CNS is responsible for learning and memory

Structural Organization of the Brain

• Contains the brain and spinal cord
• Three meninges (dura mater, arachnoid mater, pia mater) surround the brain and spinal cord
• Cerebrospinal fluid (CSF) is found in the subarachnoid space and protects the brain and spinal cord
• Different ventricles in the brain contain CSF

The Cerebrum

• The cerebrum is the "wrinkly part" of the brain
• The cerebrum is divided into lobes, each with specific functions
• Sulcus is the groove and gyrus is the fold in the cerebrum

Lobes of the Cerebrum

• Frontal Lobe: Voluntary motor control, higher intellectual processes, planning, decision making, and verbal communication
• Parietal Lobe: Somatesthetic interpretation, understanding speech, formulating words, interpreting textures, and shapes
• Temporal Lobe: Interpreting auditory sensations, memory for auditory and visual experiences
• Occipital Lobe: Visual experience, image integration, and visual memory
• Insula: Memory, sensory data (primarily pain), and visceral integration

Cerebral Lateralization

• The brain's left and right hemispheres specialize in different functions
• Right Hemisphere: Visuospatial tasks (like arranging objects, recognizing faces, and composing music)
• Left Hemisphere: Language, analytical ability, speech, writing, calculations, and comprehending visual appearance

The Limbic System and Emotion

• The limbic system controls emotional drives, including:
  • Areas of the cerebrum: cingulate gyrus, amygdaloid body, hippocampus, septal nuclei, and anterior insula
  • Hypothalamus and Thalamus
• It is difficult to control emotions because of the few synaptic connections between the limbic system and cerebral cortex
• Emotional memories are primarily controlled by the limbic system (smell brain, rhinencephalon)
• Emotions controlled by the limbic system: aggression, fear, feeding, sex drive, and goal-directed behaviors
• The hypothalamus plays a key role in visceral responses to emotions, maintaining posture, and controlling facial expressions

Memory

• Studies of people with amnesia show that the temporal lobe, hippocampus, head of the caudate nucleus, and dorsomedial thalamus are involved in memory
• The amygdala is important for converting short-term memories into long-term memories
• The prefrontal cortex is involved in complex problem-solving and working memory
• Stress can negatively impact memory consolidation (i.e, not downloading the memory) in the hippocampus and prefrontal cortex
• Cortisol release can enhance emotional memory but weaken hippocampal memory

Hypothalamus and Pituitary Gland

• The hypothalamus is critical for maintaining homeostasis and regulating the autonomic nervous system
• It controls various functions: hunger/satiety, thirst, body temperature, sleep, sexual arousal, emotions, and visceral responses related to emotion
• It helps to control hormone secretion from the pituitary gland

Hindbrain

• The cerebellum is the second-largest part of the brain, responsible for coordinating movement, posture, and balance, motor learning, and acquiring sensory data
• It influences motor coordination through the inhibition of the motor cortex from Purkinje cells

Reticular Activating System (RAS)

• The RAS is important in consciousness and regulating sleep and wakefulness
• It's made up of the pons and reticular formation in the midbrain
• Activation of the RAS promotes wakefulness, and inhibition allows sleep
• RAS activity increases during deeper sleep

Spinal Cord Tracts

• Spinal cord tracts are classified as ascending or descending and involved in carrying impulses
• Ascending tracts carry sensory impulses, while descending tracts carry motor impulses
• The tracts are organized into specific columns (funiculi) to allow for the organization of the nervous system
• The white matter is composed of ascending and descending fiber tracts that are arranged into columns called funiculi

Cranial and Spinal Nerves

• Cranial nerves arise directly from nuclei in the brain and are part of the peripheral nervous system (PNS)
• There are twelve pairs of cranial nerves
• Spinal nerves arise directly from the spinal cord
• There are 31 pairs of spinal nerves
• Spinal nerves are mixed nerves, carrying both sensory and motor neurons
• The dorsal root contains sensory neuron cell bodies, while the ventral root contains motor neuron cell bodies

Reflex Arc

• A reflex arc is an unconscious motor response to a sensory stimulus
• Components of a reflex arc: sensory receptor, sensory neuron, interneuron in CNS, somatic motor neuron, and effector(muscle or gland)
• Two types of reflex arcs: somatic reflexes (effectors are skeletal muscles) and autonomic reflexes (effectors are smooth muscle, cardiac muscle, or glands)