🧠Intro to Brain and Behavior Unit 1 – Nervous System Basics

Nervous System Overview

• Coordinates and regulates bodily functions, enabling organisms to respond and adapt to their environment
• Consists of the central nervous system (brain and spinal cord) and peripheral nervous system (nerves outside the brain and spinal cord)
• Processes sensory information from receptors, integrates and interprets this information, and initiates appropriate responses
• Communicates using electrical and chemical signals transmitted through neurons and synapses
• Exhibits plasticity, the ability to change and adapt in response to experiences and learning
• Develops from the ectoderm layer during embryonic development, with the formation of the neural tube
• Plays a crucial role in maintaining homeostasis, the stable internal environment of the body
• Interacts with the endocrine system to regulate various physiological processes (growth, metabolism, reproduction)

Neurons and Synapses

• Neurons are the primary functional units of the nervous system, specialized cells that transmit electrical and chemical signals
• Consist of a cell body (soma), dendrites that receive signals, and an axon that conducts signals to other neurons or effector cells
• Classified into three main types: sensory neurons, motor neurons, and interneurons
  • Sensory neurons detect stimuli and transmit signals to the central nervous system
  • Motor neurons transmit signals from the central nervous system to muscles and glands
  • Interneurons connect sensory and motor neurons, processing and integrating information within the nervous system
• Synapses are the junctions between neurons where signal transmission occurs
• Electrical synapses allow direct transmission of electrical signals through gap junctions
• Chemical synapses involve the release of neurotransmitters from the presynaptic neuron, which bind to receptors on the postsynaptic neuron
• Synaptic plasticity, the ability of synapses to strengthen or weaken over time, underlies learning and memory

Central Nervous System

• Comprises the brain and spinal cord, the main control centers of the nervous system
• The brain is divided into regions with specialized functions (cerebrum, cerebellum, brainstem)
  • Cerebrum is involved in higher cognitive functions, sensory processing, and voluntary movement control
  • Cerebellum coordinates and fine-tunes motor movements, maintains balance and posture
  • Brainstem regulates vital functions (breathing, heart rate, sleep-wake cycles) and relays information between the brain and spinal cord
• The spinal cord transmits signals between the brain and the body, and mediates reflexes
• Protected by the skull (cranium) and vertebral column, as well as the meninges (dura mater, arachnoid mater, pia mater)
• Cerebrospinal fluid (CSF) cushions and supports the brain and spinal cord, maintains homeostasis, and removes waste products
• Exhibits lateralization, with some functions primarily controlled by one side of the brain (language in the left hemisphere for most people)

Peripheral Nervous System

• Consists of nerves and ganglia outside the brain and spinal cord, connecting the central nervous system to the rest of the body
• Divided into the somatic nervous system and the autonomic nervous system
  • Somatic nervous system controls voluntary movements and receives sensory information from the external environment
  • Autonomic nervous system regulates involuntary functions (heart rate, digestion, respiration) and is further divided into the sympathetic and parasympathetic divisions
    • Sympathetic division activates the "fight or flight" response, preparing the body for action
    • Parasympathetic division promotes "rest and digest" functions, conserving energy and maintaining homeostasis
• Includes 12 pairs of cranial nerves that originate from the brain and 31 pairs of spinal nerves that originate from the spinal cord
• Sensory receptors in the peripheral nervous system detect various stimuli (touch, temperature, pain, light, sound, chemicals) and transduce them into electrical signals

Neurotransmitters and Signaling

• Neurotransmitters are chemical messengers released by neurons to transmit signals across synapses
• Stored in synaptic vesicles at the presynaptic terminal, released into the synaptic cleft upon the arrival of an action potential
• Bind to specific receptors on the postsynaptic neuron, causing changes in the postsynaptic cell's membrane potential or intracellular signaling cascades
• Major neurotransmitters include glutamate (excitatory), GABA (inhibitory), dopamine, serotonin, norepinephrine, and acetylcholine
• Neurotransmitter action is terminated by reuptake into the presynaptic neuron, enzymatic degradation, or diffusion away from the synapse
• Neuromodulators are substances that modify the effects of neurotransmitters, altering synaptic transmission and neuronal excitability
• Signaling pathways within neurons involve changes in membrane potential, ion channels, and intracellular messengers (calcium, cAMP)
• Neurotransmitter imbalances or receptor dysfunction can contribute to various neurological and psychiatric disorders (Parkinson's disease, depression, schizophrenia)

Brain Structure and Function

• The cerebral cortex is the outermost layer of the cerebrum, involved in higher cognitive functions, sensory processing, and motor control
  • Divided into four lobes: frontal (executive functions, planning, motor control), parietal (somatosensory processing, spatial awareness), temporal (auditory processing, memory, language), and occipital (visual processing)
  • Organized into functional areas (primary motor cortex, primary sensory cortices, association areas)
• Subcortical structures include the basal ganglia (motor control, learning, emotion), thalamus (sensory and motor relay, sleep-wake cycles), and hypothalamus (homeostasis, neuroendocrine function)
• The limbic system comprises structures involved in emotion, motivation, and memory formation (amygdala, hippocampus, cingulate cortex)
• The cerebellum is crucial for motor coordination, balance, and learning of motor skills
• The brainstem contains nuclei that regulate vital functions (cardiovascular, respiratory, digestive) and relays information between the brain and spinal cord
• Functional connectivity between brain regions underlies complex behaviors and cognitive processes
• Neuroimaging techniques (fMRI, PET, EEG) allow for the study of brain structure and function in health and disease

Nervous System Development

• Begins with the formation of the neural tube from the ectoderm during early embryonic development
• Neural stem cells differentiate into neurons and glial cells (astrocytes, oligodendrocytes, microglia)
• Neuronal migration and axon guidance establish the basic structure and connectivity of the nervous system
• Synaptogenesis and synaptic pruning refine neural circuits based on experience and activity
• Myelination of axons by oligodendrocytes (CNS) and Schwann cells (PNS) enhances signal transmission speed and efficiency
• Neurogenesis, the formation of new neurons, continues in specific brain regions (hippocampus, subventricular zone) throughout life
• Critical periods are windows of heightened plasticity during development, crucial for the acquisition of specific skills (language, vision)
• Neurotrophic factors (NGF, BDNF) support the survival, growth, and differentiation of neurons and synapses
• Developmental disorders (autism, ADHD, intellectual disability) can arise from disruptions in nervous system development

Disorders and Treatments

• Neurodegenerative diseases involve the progressive loss of neurons and synapses (Alzheimer's, Parkinson's, Huntington's)
  • Alzheimer's disease is characterized by amyloid plaques and neurofibrillary tangles, leading to memory loss and cognitive decline
  • Parkinson's disease results from the loss of dopaminergic neurons in the substantia nigra, causing motor symptoms (tremor, rigidity, bradykinesia)
• Psychiatric disorders are associated with imbalances in neurotransmitter systems and altered brain function (depression, anxiety, schizophrenia)
  • Depression involves reduced serotonin and norepinephrine signaling, affecting mood, sleep, and appetite
  • Schizophrenia is characterized by positive symptoms (hallucinations, delusions) and negative symptoms (flat affect, social withdrawal), linked to dopamine and glutamate dysfunction
• Neurological disorders can result from injury, infection, or structural abnormalities (stroke, epilepsy, multiple sclerosis)
  • Stroke occurs when blood flow to the brain is disrupted, leading to neuronal death and focal deficits
  • Epilepsy involves recurrent, unprovoked seizures due to abnormal neuronal firing patterns
• Treatments for nervous system disorders include pharmacotherapy (drugs targeting neurotransmitter systems), psychotherapy, and neuromodulation techniques (deep brain stimulation, transcranial magnetic stimulation)
• Gene therapy and stem cell-based approaches hold promise for the treatment of genetic and degenerative disorders
• Multidisciplinary approaches, combining medical, psychological, and rehabilitative interventions, are often necessary for the management of complex nervous system disorders