Brain Anatomy and Nervous System Functions

Anatomy of Brain Functions

• The brain consumes a lot of the body's energy
• The human brain takes up about 2% of body weight
• The brain contains many neurons and a complex number of interconnections between them, forming circuits
• A neuron receives information through dendrites, forming synapses and connections with other neurons

Brainstem & Cerebellum

• Perform low-level functions

Autonomic Nervous System

• Keeps the body in a state of equilibrium when the outside environment changes
• Handles automatic bodily functions
• Has two divisions: sympathetic and parasympathetic

Sympathetic Nervous System

• Involved in emotional arousal, stress, and fear
• Triggers the "fight or flight" response
• Increases heart rate, respiration, perspiration, and causes pupils to dilate

Parasympathetic Nervous System

• Facilitates "rest and digest" functions
• Lowers heart rate and respiration
• Increases stomach and intestine activity
• Opposes the sympathetic nervous system

Cerebellum Function

• Plays a role in basic movement coordination
• Sense of balance
• Coordination of complex movement
• Motor learning processes
• Involved in planning actions where the brain computes the difference between the plan and feedback during action performance
• Constantly receives sensation feedback
• The cerebellum is one of the first parts of the brain to be affected by alcohol

Brainstem Function

• Regulates body systems to keep the body alive
• Examples include regulating blood pressure and respiration

Limbic System

• Located deep within the brain involving the medial temporal lobe
• Has two main areas: Hippocampus (seahorse) and amygdala (almond)
• Amygdala is for fear/ threat learning/ response
• Hippocampus is for memory

Limbic System Functions

• Navigate through an unfamiliar environment
• Is important for survival
• Memory retention after encountering threats, to avoid similar future situations
• Remembering the location of food sources for the future

Cerebral Hemispheres - Cortex

• Most evolved parts of the brain
• Located around the frontal, temporal, occipital, and parietal lobes, including the motor cortex

Cerebral Hemispheres - Cortex Functions

• Frontal lobe is for reasoning, planning, and problem-solving
• Temporal lobe is for language
• Occipital and parietal lobes + motor cortex is for visual perception and action
• The cortex, or grey matter, is the outermost surface of the cerebral hemisphere

Cerebrum (Forebrain)

• Two hemispheres (left and right) divided by the Inter-hemispheric fissure (longitudinal fissure)
• The gap between the two hemispheres means that most of the brain's surface is not connected, preventing information flow, even if the hemispheres touch

Functional Areas

• Each sense has a primary area, connected to our senses
• Primary visual cortex and primary auditory area

Frontal Lobe

• Located at the front of the head
• The primary motor cortex is located at the posterior part of the frontal lobe
• The central sulcus, or anatomical landmark divides the frontal lobe and the other lobes behind it
• Language region
• Speaking, writing, communication

Parietal Lobe

• The primary sensory cortex resides here
• Conveys the sensation of touch in our body
• Links vision and our actions
• Gives us a sense of space and location
• Directs attention and eye-movements for exploration

Occipital Lobe

• Located in the posterior part of the brain
• Houses the primary visual cortex for visual perception
• Features higher visual areas composed of different regions
• Processes shapes, colors, motion, and orientation

Temporal Lobe

• Located on the side of the head
• Houses the primary auditory cortex for sound perception
• Contains important language areas on the medial side, where the limbic system is located
• The posterior part is connected to the parietal lobe

Corpus Callosum

• Crucial for communication of neural signals between the left and right hemispheres
• Neurons in one hemisphere send their output through the corpus callosum to connect with neurons in the other hemisphere
• Surgically cutting off the corpus callosum effectively treats some forms of epilepsy

Phineas Gage Case Study

• Railway worker injured in 1848
• Iron rod went through his head, damaging his frontal lobe
• Remained conscious during and after the accident
• Gage's physician, John Harlow, reported a profound personality change
• Became impatient and defiant
• Became overly profane
• Experienced imbalance between reasoning and animalistic tendencies
• Conclusion: The frontal lobe plays a crucial role in executive control of behavior

Wernicke’s Aphasia

• A receptive aphasia that impacts language comprehension
• Individuals can speak perfectly and fluently
• Ability to put syntax together and follow language rules is retained
• Connections between the meaning and semantics of speech are lost

Homunculus

• A map of brain functions, focusing on the primary sensory and motor cortex
• Wilder Penfield (1950s) mapped out primary motor and sensory areas
• Parts of the brain were electrically stimulated in people undergoing epilepsy surgery
• Functionally localizing areas in the brain for surgeries like epilepsy

Disorders of Consciousness

• Result from brain damage or injury
• Persistent vegetative state
  • Severe damage to the cerebral hemispheres
  • Results in no conscious awareness
  • Body functions may still be regulated if the brainstem is intact

“Locked In” Syndrome

• A consequence of motor neuron disease
• Results in the gradual loss of motor neurons; impacting connections between the motor cortex and the ability for muscle contractions to move
• Patients may have conscious awareness but appear to be in a coma
• The visual and auditory cortexes functions if the cerebral cortex is intact