Brain Structures

From Brain to Behavior: Structure and Function of the Nervous System 

  • Anatomy = Structure 

  • Physiology = Function 

  • Embryology = Development 

  • Pharmacology = Neurochemistry & Drug Action 

  • Psychology = Regulation of behavior 

 

Components of the Brain: 

  • Neurons – Where the action is 

    • Building blocks of behavior 

    • A billion to a trillion cells 

  • Glia – The support cells 

    • Form myelin sheaths, provide nutrients and oxygen, support neurons, remove dead cells & pathogens 

    • 3 times the # of neurons 

  • Blood Vessels:  

    • Nervous system requires plenty of blood and fuel (glucose) 

    • 40% of the blood pumped by the heart goes to the head 

 

Behavior is Controlled by Signals in Neuronal Circuits 

  • Reflexes – Built in response patterns executed automatically 

  • The Reflex Circuit (Pain withdrawal reflex) 

    • Central Nervous System + peripheral nervous system 

    • Reflex works through transmission of electrical signals via sensory neurons, interneurons, and motor neurons 

 

Structure of a Neuron: 

  • Basic units of the nervous system 

  • Receive, integrate, and transmit information 

  • Operate through electrical impulses 

  • Communicate with other neurons through chemical signals- neurostransmitters 

 

 

Functions of Neural Structures: 

  • Dendrites – Receives information 

  • Cell Body (Soma) - Keeps cell alive; integrates signals 

  • Axons – Transmits signals (carries them out) 

  • Synapse – At end of axon, where neurons make contact 

  • Terminal Buttons – Nodules at the ends of axons; contain synaptic vesicles; release chemical signals into the synaptic cleft 

 

  • Neuronal activity can be studied at several levels of organization (single cells, ERP, functional brain imaging, fMRI) 

  • Electrochemical communication is the hallmark of neurons 

  • Neuronal communication failures lead to impairments in thoughts, feelings, and actions 

     

Nerve Cell Communication: 

  • Membrane Potential – Charge across membrane 

    • Protein gates and pumps embedded in cell membrane control movement of ions such that 

      • Sodium Potassium Pump places more Na+ outisde axon & more K+ inside axon at rest (selective permeability) 

      • Resting Membrane Potential – The ratio of negatige to positive ions is greater inside the neuron than outside 

      • Resting membrane potential is approx. -70 mV 

 

The Action Potential : Mechanism 

  • At threshold Potential:  

    • Membrane reaches –55 mV. Sodium Channels Open to let Na+ molecules through. Na+ ions rush in until +50 mV reached. Then the channels close 

    • When membrane reaches +50 mV, K+ channels open. K+ rushes out of cell until membrane potential is back to normal 

  • Central nervous system consists of the Brain & Spinal Cord 

  • The peripheral nervous system connects to the central nervous system to the rest of the body through 2 subdivisions: 

    • The Somatic Nervous System, which acts on skeletal muscles (the muscles attatched to bone) 

      • Sensory and motor components 

    • The Autonomic Nervous System, which acts on visceral muscles (heart, arteries, gastrointestinal tract) and glands (salivary, sweat) 

    • The Sympathetic Nervous System activates fight or flight 

    • The Parasympathetic Nervous System is deactivating (Rest and Digest) 

 

The Brainstem Houses the Basic Programs of Survival: 

  • Continuation of the spinal cord into the brain; largely autonomous of the cortex 

  • Regulates a complement of Survival reflexes 

    • Gagging, breathing, swallowing, urination, etc. 

    • Cranial nerves 

    • Brainstem regulates spinal reflexes to produce useful behavior 

  • The reticular formation 

    • General arousal 

    • Induction and regulation of sleep stages 

 

Cerebellum: 

  • Important for motor function, learning, and motor memory 

  • Damage to different parts of the cerebellum effects: 

    • Damage to lobes on either side causes a loss of limb coordination 

    • Damage to the nodes at the very bottom causes balance problems 

 

Structural Organization of the Brain: 

  • Cerebral Cortex – Important in perception, language, memory, planning, intellectual and artistic function, social responsibility, emotions, etc. 

  • 4 Lobes: Occipital, Temporal, Parietal, Frontal; 6 cell layers 

  • Gray matter – Cell bodies, dendrites, synapses 

  • White matter- myelinated axons 

 

Features of Cortical Organization: 

  • Functional Specialization – Different parts of cortex serve different functions 

  • Topographic Organization – Sensory & motor areas contain a map of the receptor surface or muscles 

  • Contralateral Connections – Right side of cortex is connected to the left side of the body and vice versa 

  • Asymmetry of Higher Functions – Hemispheric specialization or lateralization 

 

Functional Specialization: 

  • Cortical Areas: 

    • Cortex (sensory & motor cortex) in mammals consists of multiple topgographically organized areas 

    • Primary sensory areas- Receive input from sensory surface 

    • Primary Motor Area- Sends axons down to motor neurons in the brains stem and spinal cord. Electrical stimulation produces twitches in a single or a few muscles 

Topographic Organization: 

  • Sensory & motor areas contain a map of the receptor surface or muscles in the body. 

    • Maps are distorted – amount of cortex devoted to each part of the receptor surface or muscles does not correspond to the size of the body part 

    • Maps are plastic,  

      • EX: training as a pianist reorganizes both the auditory and finger representations in people