Neuroscience lecture #3 (08/27/25)

Orientation and Planes

  • Dorsal = above; Ventral = below. Dorsal view = top; ventral view = bottom.

  • Anterior = toward the nose; Posterior = toward the back. In animals: rostral = anterior; caudal = posterior. In humans these terms are used interchangeably depending on context.

  • Medial = toward the midline; Lateral = away from the midline.

  • Planes of section:

    • Coronal: ear-to-ear (frontal-parietal boundary)

    • Horizontal (axial): slices across the brain

    • Sagittal: cut along the midline (medial vs lateral)

  • Orientation caveat: right/left labeling depends on the viewer’s perspective (patient viewpoint).

Afferent, Efferent; CNS vs PNS

  • Afferent = sensory input to the brain; Efferent = motor output from the brain.

  • CNS = brain + spinal cord; PNS = somatic, autonomic, enteric.

  • Somatic NS = cranial nerves + spinal nerves; Autonomic NS = sympathetic (fight/flight) and parasympathetic (rest/digest); Enteric NS = gut regulation.

  • Sympathetic neurons → norepinephrine\text{norepinephrine}; Epinephrine/adrenaline is a related but distinct system.

  • Parasympathetic dominance supports rest/digest; Enteric NS can operate autonomously but interacts with CNS states.

  • Core purpose: receive environmental information, integrate it, and produce appropriate movements.

Contralateral vs Ipsilateral

  • Contralateral = signals cross to the opposite hemisphere; Ipsilateral = same hemisphere.

  • Cross-hemisphere connections typically involve the corpus callosum; ipsilateral connections stay on one hemisphere.

  • Orientation notes: hemisphere labeling can be from the patient’s perspective, which can be counterintuitive.

CNS and PNS Organization; Dermatomes

  • CNS vs PNS recap:

    • CNS: brain + spinal cord

    • PNS: somatic (cranial + spinal nerves), autonomic (sympathetic + parasympathetic), enteric

  • Spinal nerves: 3131 pairs; regions: cervical, thoracic, lumbar, sacral, coccygeal.

  • Dermatomes map skin regions to spinal nerve roots.

  • Cranial nerves: 1212 pairs; originate from hindbrain; mainly motor/sensory for head and face.

  • Notes: memorizing exact numbers is not essential for this course; focus on functional roles.

Brain Lobes; Gyri, Sulci, and Key Landmarks

  • Lobes: frontal, parietal, temporal, occipital.

  • Central sulcus separates frontal lobe from parietal lobe.

  • Precentral gyrus = primary motor cortex; Postcentral gyrus = primary somatosensory cortex.

  • Gyri (ridges) and Sulci (grooves); Fissures are deep sulci (e.g., longitudinal fissure).

  • Longitudinal fissure = separates left and right hemispheres.

  • Major gyri examples: superior/middle/inferior frontal gyri; superior/middle/inferior temporal gyri.

  • Corpus callosum = major white-matter tract connecting hemispheres; approx 2×1082\times 10^8 nerve fibers.

  • Anterior commissure connects temporal lobes; Posterior commissure is another midline connection.

  • Gray matter = neuron somas/dendrites; White matter = myelinated axons.

  • Ventricles and cerebrospinal fluid lie below the corpus callosum (CSF-containing spaces).

Quick References and Tips

  • When describing brain regions, use lateral vs medial and superior vs inferior relative to the structure being viewed.

  • Orientation concepts recur across modules (dorsal/ventral, anterior/posterior, rostral/caudal).

  • In exams, focus on functional roles of major regions and the direction of neural pathways (afferent vs efferent).